I'm planning on installing headers and an open air cleaner on my 305 Qjet carbed car (85 firebird,) but I heard it it will affect cold starting and drivability.
The temp here is usually around -10 to -30* C. Will it give me any problems?
Its a perfect bike for you. Its really really cheap if you drop it (scratched plastics, who cares?) and they really are not overly power full. You can also buy a lowering kit and a lower seat for reasonably cheap. Its definitely not to much bike for you.
55MPH is no problem for the bike, and it will still probably accelerate faster than most econobox's. If its in good shape for a good price buy it, but avoid 65+mph highways and freeways like a plauge.