(XS) Extra Small: 2 - 2.5 inch nursery pot.

(S) Small: 3.5 - 4 inch nursery pot. 

(M) Medium: 5 -6 inch nursery pot.

(L) Large: 7 - 8 inch nursery pot.

Your plant will do well in medium-level humidity. It should be fine with the humidity level in most homes however if you live somewhere particularly dry you may want to consider adding some form of humidity to your plant care like a pebble tray filled with water, or you could try misting your plant once every few days. Things like heating systems can cause the air to dry out unnaturally so make sure you keep your Peperomia away from these.

Yes

Allow the soil to dry out partially between waterings. Feel the top two inches of soil and as it begins to feel dry to touch give this plant a drink.

Medium to bright light to maintain their vibrant foliage colours. Direct sun rays should be avoided, as it can burn the leaves and can cause the markings on the leaves to fade.