how big is the difference between Polish RC and regular(vatican)
There is no difference. There is only one Roman Catholic Church, and its head is the Pope in Rome (the Vatican).
How much of the service is Latin as opposed to Polish?
It's all in Polish.
If married in RC church in US, would Polish RCC require remarriage?
This is gonna be guesswork (sorry) but AFAIK you would only need a sworn translation of your marriage certificate. The same goes for baptism, confirmation, and any other sacraments.