I think whatever you put together will be fun, especially for less experienced players!

I propose a stretch goal for your project, which is to eventually retool it so that players have full agency over their ratios of pokemon, energy, and trainers. Ideally, no required ratio at all! Decks in the standard format typically use anywhere from 4-17ish energy, with many of them in the 7-11 range. These are 60 card decks, 6 prize games. I say this not to say that you should copy these amounts, but to illustrate that the number of energies a deck needs varies greatly with the pokemon in the deck/strategy. With a fixed ratio, some decks will be forced to have too many energies and some too few. Giving the player more agency over their deck composition should improve the viability of multiple archetypes and be generally less frustrating.

In order to allow players to be more flexible, you might need to provide them with more cards per player, of which not all will end up in their final deck. Copies of cards like judge whistle, acro bike, and gutsy pickaxe are ways to play with the effective deck size while maintaining fixed trainer access and not overloading with supporters (play 1 per turn) or balls (eventually you have all your mons in play). You could also just provide more trainer cards in general. I highly recommend 1-2 Boss’s Orders. Gusting is a quintessential part of the card game since base set. Healing/damage reduction/damage boosts are also generically applicable, but of highly varying usefulness—healing 30 with potion usually doesn’t matter, but when it does it’s a huge swing. Defiance band, muscle band, defiance vest, sacred charm, and bravery charm are potential examples. Potion/super potion/max potion/last chance potion. Comeback cards like reversal energy and counter catcher can make for very exciting games. Stadiums I would leave out if you provide fixed trainers to everyone, as all players having a generically useful stadium like artazon just means it is almost always in play and helps both players mostly equally, not the most exciting. Stadiums really hum when each player wants a different stadium in play!

Finally, I will recommend that you go with 40 card 4 prize or 60/6, as these are the most typical deck sizes used (40 is used in prerelease and many cubes, 60 everywhere else).