Do the bonuses provided by Blessed by the Emperor and Warlking the path stack with each other? (both the bonus to WS/BS and the penalty to the enemies BS)?
Can a character with balanced weapon in one hand and defensive weapon in the other hand use them to crossguard for +25 bonus to his parry?

Do the bonuses to tech use from combi tool and MUI stack with each other and is there some other gear needed for an explorer to link himself with the spaceship using a MUI implant or the ship is assumed to have what it takes for that to happen?

Psychic question: No. Check page 158 near the bottom under Cumulative Effects

Weapons question: No. The bonuses by that weapon are only for use by that weapon. Pick which one you're defending with and use that one's bonuses and penalties for Parry's Weapon skill test. You also don't get a best craftsmanship's +10 to weapon skill and +1 to damage to weapons that aren't that one.

Combi/MIU: That one's a little more up in the air, and I'd say it depends on what exactly you're trying to do. My reading is that the MIU is more of a computer thing, while the combi-tool is more of a mechanical thing. If it's a situation where both can help, then yes, if not then no.

I'd allow them to stack Tech Use for repairs, since the MIU might help you get a better idea of what's wrong and what needs to be done and the combitool helps you do them.

If you're trying to use Tech Use to interface with a ship's Core Cogitator and download some information then the Combi-tool isn't going to be of much use.

As for which objects or ships have MIU plugins and which don't, that's never really explicitly stated. On a voidship, I'd say they definitely have MIU plugins, but only in the places you'd expect them to be, like the bridge, engineering, core cogitator, etc.

Yes, the MUI/Combi tool question was specifically for the needs of performing repairs on the voidship. We are lacking an explorator as part of the PC crew and our ship is mars reliquery so our Heretec Rogue Trader is looking for as much assistance with fixing the ship as he can get his hands on. Thanks for the information.

Yes, the MUI/Combi tool question was specifically for the needs of performing repairs on the voidship. We are lacking an explorator as part of the PC crew and our ship is mars reliquery so our Heretec Rogue Trader is looking for as much assistance with fixing the ship as he can get his hands on. Thanks for the information.

So is he repairing the entire voidship himself, or is he simply leading the repair crew? If the latter, does the majority of the workforce have combi-tools as well? If not I'd probably say that it doesn't make much sense for the combi-tool to provide it's bonus (an entire voidship is probably a little outside the scope of a single combi-tool)

I'd suggest that you look to acquiring a skilled NPC who specializes in that sort of stuff.

Yeah, if you aren't assuming that the ship already has Tech-Priests capable of maintaining the ship, using the typical crew rating of the vessel for their Tech-Use, sort of like if you don't have a Navigator PC, then a heretical RT should have little trouble finding a heretek, maybe even a minor arch-heretek, for his money, and the quality of the ship, to oversee things. Once the RT becomes "open" to alternative ideas of their crew, finding those weird crews can actually be pretty easy. If you want a more traditional Explorator-analogue, say your RT is more "not in support of the Ecclesiarchy" heretical, purchasing a quality Tech-Priest should be a little tricky, the fun kind of tricky, which involves some RP searching, and maybe a handful of good rolls, but overall quite doable, sort of like looking for a talented soldier, or a particular accessory for your ship.

If you are trying to avoid the Mechanicus, all together, I suppose you could, but it will probably simply get replaced with Mek Boyz, Earth Caste Tau (depends on your game), or something else; it'd be pretty strange to just have laypeople able to maintain a voidship to the degree a Rogue Trader would require, though interesting, now that I think of it.

Hmm... haven't considered the fact that all the assisting tech priests, but it makes sense. How many tech pirests would you say are there on a void ship (as hard number or percentage of population) and how many of them are busy with repairs with the rest taking care of standard maintanance and operation of the vessel. Does a platoon (10-30*) for emergency repairs and company (50-100*) for extended repairs sound like a good number for a ship of the size of our Orion clipper?

We do have minor tech-priests on board at the moment, but I'm not sure if after they learn about the heretec tendencies of our Lord Captain if their loyalty will stay true or we will have to jettison them in the void after small on-board civil war. But regarding the replacement ideas... although they lead themselves to a lot of roleplaying opportunities... I'm not sure how viable are they. I guess if I get my hands on a hulking power armor, my brute mutant missionary can keep them in check, but we will soon end with unreliable ship ordinance, and without master of gunnery behind the trigger it can spell alot of trouble.
The tau earth caste sounds like a lot safer option, but how does one end up recruiting tau? It's not like we can just buy them from the ethereal that accompanies them and if we "take care of him" we can hardly count on them not deciding to do one final sacrafice for the greater good while being around our plasma drive. Other than that I assume Tau won't be really familiar with Imperial technology, but considering their scientific rather than dogmatic approach to the problem - they should be able to learn in relatively short amount of time.

* I'd assume that the actual number of bodies involved in the process are more than that, but the rest are servitors that are doing the literal heavy-lifting rather than participating with their tech skills

As an eyeball on how many total tech priests per ship, I'd say about 2-5% (about 1 in 50 to 1 in 20) of the crew pop (meaning about 280 to 700 total).

https://community.fantasyflightgames.com/topic/78289-how-many-naves-astropaths-and-priests-are-on-your-ships/?p=867241

It's another one of those fun numbers, like the Astropaths, Navigators, and sometimes total crew; how many are there on your ship? At least the Rogue Trader is easy; barring a slightly weird game, or guests, there is one For Tech-Priests, it can also be "how many AdMech are there who are privy to the secrets of starships?" Some, I suppose, will be just your typical Tech-Priests, who know how to minister to, and repair, stuff, but there need to be some who know how the warp drive works, or archeotech __________ you have. For the AdMech, though, while still a minority, I'd put their number up higher than the other "specialist" types; there's a lot of ship, even the small ones, to maintain. An actual number, so anything I said might be helpful, I'd need to think on.

Actually, I don't think numers need to be TAHT high. Even the lowest Enginseers probably command scores of servitors, cyber-cherubim, servoskulls and lay-technician crew.

Certainly true, also. Your ship might not have a swarm or actual Tech-Priests/Exploarators, but each will have access to numerous monotask servitors, able to do some work, and assist in other, and, unlike quality Tech-Priests, Servitors can be rather easy to acquire en mass. Even that being the case, though, I prefer to assume that there are more Tech-Priests than Astropaths, or Navigators. Neither of these can usually be "made", but need to "naturally" occur, while Tech-Priests can be trained, and augmented. Unless Navigators can Assist one another, there's only one place they do something, and only one at a time; you'd have others, but more as back-ups, or rotation, so less than a dozen. Psykers you know about, I'd guess maybe a dozen, if you can pull some serious strings, and arrange for a full Choir; after that, "extras" might just be a waste of resources. Big ships, though, might need two or three dozen, so one can oversee a large area, and monitor the Servitors there, while others might conduct some research, or what have you, and the usual rotation. Many of these might be no better than your typical Enginseer, as composed to a full on Explorator, hoping to someday become a Magos, but still. This is, of course, mostly just my opinion.