I didn't vent the air in the medbay or cockpit. I vented everything except that, and then when my O2 system got destroyed by the enemy ship, the medbay and cockpit ran out of oxygen as well.
Well that`s the risk right. If you vent and stick the crew in the medbay until the boarders go there and then take hits in the doors, O2 or both it`s gonna be pretty hard to salvage the situation. But with more experience you`ll remember to look at the weapons array of the ship you`re facing and adjust accordingly. If there`s no sun to worry about and the enemy has ion weaponry and no missiles you can probably just run the whole crew into the medbay and vent the rest safely. If the enemy has missiles or powerful lasers then you`ll probably be better off venting one room at a time to herd the boarders around a bit. One of my personal gripes about FTL is that the enemy ships never vent you when you board, making a player boarding strategy a bit OP.
As for the suns unless you are under threat of taking hits in the doors or O2 from an enemy ship it can be effective to vent all the rooms in the ship not occupied by someone to reduce the area fires can start in while the FTL charges. Again though you might wanna keep the door room oxygenated just in case a flare blows out the system, which it will on occasion. Also, upgrading the doors and o2 supply will make it less likely that solar flares will knock them out and it pretty cheap to do early on.
But it`s almost all situational is the main point and why I like the game. There are many very bad ways to deal with most problems and lots of good ones, and because you have so many moving parts it all gets quite complicated and strategical. Of course you`ll have bad luck sometimes and narrowly flee something impossible only to land somewhere even worse and die. Sometimes blind alleys appear where you`d think there should be a path, forcing you back into the federation fleet, which is fine after zone 5 or so but hardly in zone 1 or 2. Sometimes you just cannot find a weapon no matter what you do and die pathetically somewhere in zone three when your starting weapons can`t break enemy shields anymore and just an endless number of similar things that have the potential to go bad on you without warning.
As for the FTL forum elitists, I once played a game where I died halfway through zone 6 without having found a single store. So how people can claim it`s possible to win 99% of games I have no idea. Skill and experience matters yes, but sometimes random acts of sabotage just won`t let you win no matter what you do. So unless these braggarts have a cheat for the game or something that lets them avoid all the randomness normal people experience, or simply pretend their games ending in zones 1-4 never happen so as not to mess up their shiny stats, I refuse to take these claims seriously.