In my opinion King Airs are the best turboprops ever made. Having said that I would be very careful buying one especially the 90 series, there are simply too many different options to know for sure if you are getting a good deal or not.
Consider this; there are A90's, B90's, C90's, C90A's, C90B's, and F90's. On all those airplanes you can have PT6-20, PT6-20A, PT6-21 or PT6-28 engines. They all produce between 500-550 hp. In addition the ORIGINAL overhaul on a PT6 engine is 2500 hours, MOST King Airs have had the AD done that increases the overhaul period to 3000 or 3600 hours. Bottom-line, you're probably better of hiring true, professional broker that knows the differences. Bubba at the FBO (who's bought a couple of Mooney's) isn't going to cut it.
Your questions: Usable load about 3300#'s, fuel capacity is 2563#s or 382 gallons. So with full fuel you can carry about 800#'s. IFR range is around 1000nm, obviously depending on winds and altitude. If you're hopping around down low, you have about 3 1/2 hours worth of fuel, if you can get up to the mid 20's you can go for about 5 1/2 hours. The difference between 90's is almost not noticeable, fuel tanks and some electrics, are about all I can think of. They all perform the same IF you they have equal engines (i.e. an A90 with -28's will perform the same as a C90B with -21's).
A trip from CRQ to OAK, will take you 2:02 using SID's and Stars, you'll burn about 140 gallons (S. Cal Jet A average $2.50 per gallon) cost about $350 for a 1 way trip to OAK.
The problem with going to school is that there are almost no 90 Sims around, FS LGB has a 200 Sims, so for the most part you will be playing in the 200 Sim then taking an hour of differences for 90 stuff (which is pretty worthless), I think FS ICT has a C90B Sim that is level D and has EFIS, etc, but what good is EFIS if your A/C doesn't have it.
For maintainance Raytheon has a facility in VNY, but the better one to go to is in LAS. 200 hour inspections cost about $16,000, props cost $12,000 (I can't rememeber the time interval, Hot Sections cost $50,000 @1500 hours and Overhauls cost $100,000 at 3000 hours (depending on what AD's have been complied with this can be 2500 hours to 3600 hours), in addition you can put the engines on the MORE program elliminating Overhauls (don't buy a King Air on the MORE program, its not a good thing).
Flying in SOCAL look for an airplane that has TCAS, hell, INSIST on it!
Insurance will cost a minimum of $11,000 annually, going up drastically if owner flown!
The 90's are all great airplanes, Cmd Taggart, you should really try to get that job! Absolutely no reason you shouldn’t, just hire an ICP to get you through the first couple months.
Good luck, selling the airplane, people love to TALK about buying an airplane, but most never sign the dotted line. Something about putting up the money makes the BS walk!