So after beginning, characters find new equipment. How can we determine to which weapons there are already MIU ports (DM can rule of course some to have). And which weapons can be fitted with MIU port with Tech-Use or similar skill?

Specifically are there weapon type restrictions? (Other than primitive IMHO)

Are there weapon manufacturer limitations?

Are there weapon quality restrictions?

Waepon size limitations? (If used normally in hand, shouldn't be any other than your characters limitations?=

Other limitations to prevent a weapon from having a MIU port?

Can tech priest mount a weapon without getting the weapon miu ability as his is already more advanced? (If not what does he hav to do to mount it for example to shoulder? Tech-use to make a shoulder mount for the weapon or elsewhere? If materials are readily available?)

And this context is with a TECH-Priest with good quality MIU port, who is able to link to weapons with MIU port and receive +10 BS with MIU linked weapons.

Basically, any weapon made for infantry use will not be MIU-able without parts that let it interface with an external controller, which means rebuilding the firing mechanism from the ground up. With the correct parts, an MIU can be used on anything you can carry. So, the short answer is: With enough tinkering, you can use whatever you like. Careful of tech heresy though!

More specifically:

An MIU uses an existing, integrated mechanism in the weapon that normally relays to a remote control device elsewhere, such as found in bunkers or tanks. This means, with your MIU, you should be requisitioning bunker or vehicle versions of things such as flamers, heavy bolters etc. rather than the normal infantry models.

That said, it is likely that the admech have their own MIU version weaponry called "integrated weapons". By principle, they are the same thing as an MIU. The problem is, the rules are a copy paste from the Lathe Worlds supplement and they're virtually useless. As far as MIU-able weapon types go, though, anything that can be integrated cybernetically can probably be MIU'd. MIUing it is mechanically superior, so, MIU it.

Thank you, for the clear answer

No problemo