Most taps will fit, yes. Perlicks definitely.
No real need to replace your font, unless you want to, of course. You can always take the font out and clean it when you're doing your tap upgrade - but obviously your beer doesn't touch the font, so no biggie as far as beer is concerned.
I'd imagine spirits will be fine in an all stainless font.
Re: taps. 500-series taps have been discontinued. You can still find stock, and they're reasonably good value, but that's because the newer, improved 600-series are now out.
630SS are stainless standard and 650SS are stainless flow control (some leaking issues have been addressed in the 600 update).