1) Shields Does not seems to impact boarding party strength, nor weaken the defenders, at least it never did in the many times i did that, we talk about 60+, stopped counting

2) Hull integrity does not seems to influence the defenders either, although it reduce the ship value on sell

3) Never used officers, bonus too low for the price, prefer the commander skill, it effectively strengthen your marines combat skills significantly, even if only to a point

Hacking skill does weaken the defenders, but only if active on the ship you are actually boarding and sometimes, only if you activate it when specifically targeting the ship. Pretty much if it was active, disable it and then target the ship you want to board and then activate it again, otherwise sometimes it evidently work, other times...not sure, may be a glitch, probably

Also the level of the life support sabotage level must be significant to notice any relevant bonus, at least 20% or more

4) The number of marines a ship can carry is fixed in SG2, perhaps in the 3 ships designs will be upgradable...for now either you buy or steal a bigger ship, or mod the game to increase the number of marines your ship can have

5) Rare drop when raiding other ships, otherwise no. But if you want to use boarding as a source of income, remember to get the commander skill to at least level 2, that will turn boarding a profitable activity, as bigger ships can sell for 6 million or more if intact, easily cover the cost of replacing marines

Also for boarding, i would suggest getting a ship capable of cloaking, as boarding do not disrupt the cloak and make the whole operation a lot smoother