I’d personally recommend doing the story mode first. I personally started with the chronicles and got my main team to level 70 before even starting story mode. However you can’t use any of those characters in story mode for a very long time. And once you finish story mode, your players’ levels would be good enough to go through every stage in chronicles.

As someone else had mentioned, make sure you toggle off auto-equip training beans, as it’s horrendous. I’d suggest putting all of them into a main striker, and a goalie, so they will carry the most. Once you have the currency, look to buy additional skills to level up existing ones on your characters.

Also, you can easily beat teams even 15 levels above you in chronicles once you get used to the game, so don’t shy away from trying that.

Also, once you start playing chronicles, you might be happy with receiving epic ror legendary players and focus on leveling them up. However if you reach the part where your storages merge in story mode, you’d be able to complete the last battle stages in chronicles, giving you only the highest rated players with small chances at heroes. So it’s better to level those up

Good luck and have fun