best use of money: Save it for gambit and buy as many pink key/n-gatcha bundles as you can. once you reach 1k keys you stop getting them from battles and instead get more caches. Also sometimes they have useful bundles you can buy with them so its a good idea to save up as much as you can.

Kurito: R-gatcha are the main thing for kurito's nest either 1 or 3s. There's also a few other things like glasses that you can use but without have a good bank of them I wouldn't recommend using them.

Exploration: Some people stick around in the first area for awhile but you've probably already moved on. You can stay around in the same area until you've found the Sr for it but don't have to since it will come up eventually in the bonus explore or GHQ areas. Also GHQ/bonus area have some cards that are exclusive to them so its a good idea to progress and you get the R-card of the girl for each area you complete.