I have in the past held some disjointe unorganized sessions just for some brief fun but now I've put in some effort and bought rescources for saturday so I wondered if I could get some help me develop it:

The characters start on a slave ship heading for a mining colony, the ship is led by a pirate lord named Archeus, the slaves are in cells of five the prisons are rather basic as a result of being a new addition it lacks any particular sophistication outside of electric locks. The cells are located in the lower mid-section between two military quarters the hangar is at the end of the ship and the navigation is at the upper part of the midsection while medical, storage, civilian quarters and command. It is a relatively small ship enough to sustain a force of three hundred men with five hundred in civilian personal two hundred of which happen to be prisoners. The military personal outside of the officers are equipped with stubbers of a variety while the officers are as a rule equipped with swords, normally high quality or chain, the rest, outside of those with wealth, are equipped with knives and improvised weaponry. Each of the military quarters have their own mess halls as well as armory’s.

The ship is a week from its destination and the electronic looks can be opened by data slates that are held by any prison guard. The characters should focus on getting out and infiltrating one of the quarters surrounding them alternatively they could secure an exit and rally the rest of the prisoners however they are outgunned, outnumbered and in a bad position. Archeus has his own personal quarters next to the command center and within it he has three rooms his living/trophy room, his personal chamber and the chamber of his concubine. The officers sleep in the same quarters as their men though have their own rooms roughly 10x25 meters and allow for some privacy and personal life, civilian personal works the same way however they have been increasing as the men have formed families causing Archeus to consider purchasing a new ship or expand the old one to accommodate the expansion of his labor force.

The navigator is located above the hangar and has a better room than most being 15x30 meters but that also includes workspace. The navigators name is Morduth and is from a small navigator house of little renown and is as such a nobody among other navigators however onboard the ship he still possess a great deal of respect from the crew and has gotten them out of quiet a few tight spots.

What I need help with is primarliy the initial escape as well as a segway into the "rivals for glory" adventure from the GM's kit.

Now I havent got the GM Kit so I dont know how that starts off to lead you into it but I can suggest ways out of the ship.

A good possibility for escape could be a raid. You could have their prison ship attacked by ships of a chaos warlord seeking slaves/conscripts for his growing hoard so chuck a few crack troops, traitor marines etc. or probably Dark Eldar looking for easy souls The minions on board a penal ship would likely have a better chance there than whatever hell hole they would originally be on. Just because it is a pirate does not mean that he will not be preyed upon by bigger fish. I mean it's just a slave ship not a **** war ship that a lord might have at their disposal.

In all the confusion you could quite easily allow a group of players to slip away/be conscripted etc and play further into any other campaign once the ship command is up for debate.

The GM kit provides an adventure that is more or less a tresurehunt a big shot trader shows up and offers you information about a relic having given up on it himself

Hmm so based on this you need a way of having someone offer you an opportunity somehow. I think that could be your way in then.

Bigger shot pirate/lord wants people to help him find the relic and doesnt want to risk his own crew, goes looting a crew of slaves...

Just think "O brother where art thou" except have the protagonist die during the escape.