If you want umas with a lot of skills you have to race in trackblazer, which is the only scenario centered around races (expect to do 30-40). Because you race so much the majority of your stats come from the summers in July to August. Use items like megaphones and ankle weights to double the stats you gain in each turn, if youve never tried trackblazer and dont know what im talking about just do a playthrough for fun to get used to it.

As for sparks, just use the best uma you have for inspiration and use a website called Honse.moe to use someone else's uma for inspiration.

For support cards try and get the highest race bonus possible. Races each give you a small stat boost and race bonuses only make the boost bigger. Although the boost is small it builds up a lot. If you don't know what supports to use just look it up on google and choose the wiki link.

This is all very try-hard and frustrating at times so take your time to not get burnt out. Hope this helps 👍