650 hp huh, thats quite alot of power.
On the road i think you will find that undrivable, for a rear wheel drive car you will spin the wheels whenever you nudge boost. But thats just my opinion.
Yes if you tune it to 98-100 octane then it will be fine.
Yes you would definately need a re done rb25.
I'm sure you would get used to driving on the right hand side but it would be weird, check that it is legal too.
You would need one massive turbo, a new full ecu, definitely a twin plate clutch, maybe 2 fuel pumps and 1000 cc injectors