You can tell how many pots it is by looking thro the wheel spokes. If you can see a claw over a pad then it's a single pot sliding caliper, the pot is on the inside behind the disc and you are looking at the sliding bit. If you can see a single round bulge in the casting on the outisde then it's two pot, there's one pot on the outside and another out of sight behind the disc. If you can see two round bulges in the casting on the outisde then it's four pot, there's two pots on the outside and another two out of sight behind the disc. If you can see three then it's a six pot and you are very lucky
For diameters then I can only suggest a tape measure....