I think that level 62 for the Diet Building is cutting it a little close, but you should be able to manage if you play it right. Though I can't really say much. I was level 70-something after beating the 5th Kalpa before I entered the Diet Buliding, so everything just rolled over and died.
Meeeh, it's more or less that I barely edged out Ongyo-ki and the Moirae sisters before railroading everything until Trumpeter, who plastered me so hard I dropped the game. After leaving it sidelined for years, the endings were spoiled to me, and just decided to leave it be.
I can understand that. The Trumpeter has a really aggravating mechanic. Unavoidable deaths are stupid, and he healed himself back up to full 3 times in a single fight against me.
I'm just going for the True Devil ending because it's the hardest.
Edit: 1.5 hours in the fusion chamber just to get a mitama with Pierce, Rakukaja, and Prayer has taught me that Devil Survivor's system of choosing which skills to inherit from a list was just them fixing really bad game design. I honestly cannot think of any merit in making me sit there and reselect demons over and over just to get the skill combinations I want.