Regarding pot "size", it depends which dimensions you're talking about:
Shaft
diameter is either approx 10mm (US pots) or 8mm (metric pots - Japanese, Korean).
Shaft
length varies a
bit, but the ones used in Strats, Teles, SGs etc are pretty much a standard length - the threaded part is roughly 3/8", at a guess. You'll also see pots described as "long shaft" (about 3/4") which are really
only needed for Les Pauls because of their thick, arched tops. Some LPs have multi-depth control cavities so standard pots will fit - take your old ones out to check!
The size of the
main body of the pot doesn't really matter as long as there's room in the control cavity, but a standard pot (US or metric) is about an inch wide. You also see miniature pots, mostly in import guitars, EMG use them too.
Here's a diagram for a treble bleed cap:
http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=treble_bleedThe resistor is optional, and you can experiment with cap values. I think Fender use 0.001.