Honestly, on normal you can finish both games by level 3x quite easily, really. But if you are going for 100% you will end up at roughly 40~50x for KH1 and 50~60x for 2.
If you actually want to defeat the hidden bosses like Sephiroth or do the Org Fights in the Cave of Remembrance on 2 then you will want to grind to level 100 (or spend a few hours learning patterns and getting actually good at the game, since those are the only actually hard parts of normal KH2).
But you can easily do everything else minus those fights without being lvl100. Synth will take you a while, but it's more annoying than it is hard (I personally hate the gummi stuff so i just skip it lol)