You get heated seats with the winter pack on cloth.
As for 510, I went for the 310 as it was specced in the car I bought (couldn't be arsed to wait for a factory order, got 99% of what I wanted from a stock car). However first thing I did was get a 510, the 310 doesn;t look good at all with the rest of the GTI interior, i'd say defo go 510 but maybe don't get the dynaudio?
As for colour, completely personal choice of course, I love red, white, black.