Hey there! Question #1 is hard for me. A wingman and I were at the Alien Ruins site and decided to let our crewmembers have-at-it. Mine was an Expert(leveled from Mostly Harmless) Taipan (fixed beams/Heat sink launcher) and his was a Mostly Harmless Condor (fixed multicanon/chaff). When we told them to attack from real close, mine took out his. However, when we told them to attack from 5km+ away, his took out mine. His crewmember was able to compensate for the Condor's weak vertical thrusters on the surface, even at Mostly Harmless combat rating.
Question #2, I found in combat zones my crewmember would go through fighters fast, and a size 6 hanger would deplete before my weapon ammo would. Equipping a size 7 seemed to let me stay in longer.
Question 3#, For me yes. Starting from a mostly harmless crewmember ends up being cheaper in the long run because their pay starts lower. Helping them increase rank doesn't take too long either, just an hour or two in a High res in a high sec system (like Sol) can gain them several ranks. If you carry around engineer cargo through high security systems you're bound to get a lot of pirate attention and help from system security

I role-play a bit, and so I found a buddy with the same first name as me in Maia. Got him all ranked up so that I had a good feeling hopping in the fighter and having a Deadly Corvette watch my back[up]