#1 You're not going to find crap for $50K in the way of a twin (or anything people will want to charter for that matter).
#2 I looked at the operating costs with my old man between a single and a twin. You're looking at 4 times the cost overall, for not much performance. Twice the systems, twice the enges, twice as much stuff to break. 2-3 times the fuel burn for a few more knots when comparing like a/c like a Bonanza to a Baron.
#3 If you really want to become poor, just burn your money. It'll be a lot less painful than trying to run a 135 operation on one airplane.
As far as a C-310 being a trainer, it absolutley is. However you're looking at serious operating and maint cost. Yeah it's fast, but speed is relative. Your brain and habit patterns will catch up. I remember climbing into the mighty T-45 thinking I'd never be able to hold on climbing out at 250+ knots. After several years in the F-18 I'm beating my head against the canopy when I'm below 10K and 280.
On another note of lookign at Cessna twins, look into the ADs. There are some expensive ones out there, a few that are recurring.
If you want something cheap to own/fly for your own amusement, look into the experimental market. You can get a nice Glasair for 50-70K that will run 200mph all day long. Or a Long-ez that'll run 170 TAS on 6 gph.