Where can you check your current amount of stacks?

I don't completely agree on the "don't invade the enemy jungle" bit. It's given me great results on most of the games I've played, with the occasional exception - as Catherine, I aim to first secure the twin creeps next to the jungle market by the enemy side (I'm usually there by the time they spawn), then go back towards my own side. If I see an enemy already there, depending on who it is and if I have a teammate nearby, I may choose to engage or retreat, but it does give me a...

Sometimes I'll ping green without meaning to, right after closing the market and trying to exit the base at the start of the match... Don't really know why, as my fingers are nowhere near the upper right corner!

If I understand your question correctly, you need to choose the appropriate symbol (upper right corner, the "x" symbol) and then tap on the location you wish to indicate as "no go" (as that's what that symbol means, in-game). The mark dissapears after a short time. You can press on the mini map after selecting the symbol, if you're away from the location you wish to point out.

The longest match I've ever had (we're talking over thirty minutes long) was also the greatest comeback, ever. So it's Catherine (me), Petal and Glaive vs Koshka, Skaarf and another Catherine. As the match evolves we're clearly overwhelmed, with the enemy team quickly gaining control of our jungle as they push me and the other jungler (Glaive) back constantly. Our laner does what Petal can, and we even manage to take out a turret in the process, but soon enough the enemy team gather...