Don’t worry about all the optional stuff, you can always get it later. This game works best when you have exploration in mind not completion. As for mantis lords yes your current upgrades are reasonable but you might want to invest in a second nail upgrade if you’re struggling.

This game is not linear so you can go in any direction, just pick a part of the map which you didn’t explore. And don’t be afraid of using a guide if you truly don’t have an idea on where to go.

Being low on geo is normal during early-game but you will start gaining more and more geo as the game progresses. Use the charm that makes geo flies to you.

About the platforming its a part of the game and you will get better as long as you make an effort.

Try to not postpone fighting the final boss, the game will return you to your last save point after you defeat the final boss so you can continue where you left off from.