1. From what ive read on these forums the series 2 has a quicker spooling nylon turbo, different front\bonnet\lights, maybe other things but i dont know.
2. just make sure u get it looked at by a good mechanic, get pressure tests done etc, bring someone with you maybe that knows skylines, take it for a spin make sure u like how it drives..
3. normally boltons yeah, exhaust, aftermarket ecu, intercooler, boost controller should bring you close to 200rwkw