Well, as for starting levels, the max is/was 10, so... moves that you'd know by level 10, certain egg moves (for example, I'll let in Ice Punch on a Riolu, but I won't allow Volt Tackle on a Pichu, due to how powerful that move is), and some moves that could be from whatever 'differences' you'd like to have on your character. (for example, a charmander that's somehow also an ice-type might know Powder Snow, as well as ember, but one that's an ice-type INSTEAD of a fire type might only know Powder Snow.)