Pokécharms

Can you elaborate on the question a bit? (also, the word you're looking for is 'allowed'. Just for the record ^^)

Like moves, items levels, etc. Things most commonly used in a Pokemon battle.

It is helpful to treat an RP as a more realistic representation of the things that happen in the games.
Take levels and stats for example - base stats and particular training in certain fields would certainly count for what a Pokemon can or can't do well, but you can't get quite 'exact' on it based on a calculation of levels.

Type advantages obviously apply, but the turn-based battle mechanics may alter somewhat considering the fact that this time, it's two (or more) mobile creatures in combat, utilizing their environment, dodging, building themselves into emotional fervor, affected by their physical state and what have you.

Items may be held or used - the restriction of one hold item per pokemon applies mostly likely both to prevent encumbrance and due to official league rules (i'd imagine that unofficial and underground battles not bound by the standard league practice, for example, might have ways around this, but then that is questionable practice).

The four-move restriction from the games makes sense in building strategy/tactical limitations... in the games. But on actual creatures it'd be absolutely nonsensical. However, some RPers insist on it, so that specifically depends on the RP you're in.

Oh yes. Pokemon are obviously restricted to their learnsets in terms of moves they can or can't learn so long as said learnsets are compatible with the games as they are currently. This means that if there's a move that a pokemon could learn, say, only in generation 3 but can be carried over into current generations through various iterations of pokemon bank or what have you, it's fair game.