Try not to use a voltage above 12 or so unless you want to run at TGV speeds.
As far as #3, if you cut below the belt line and then glue them to the seats. I would use S scale 1/64 scale people; it seems that 1/48 people are too large for O scale seats! "It looks to me like the amputations will show through the low windows", not really; well, unless you really stare at the car at eye level. Not to mention, real people come in all sizes.
