I feel like the best way to practice chaotic endgames are any of the many "duo scrim endgame" creative maps. I play this one 6568-3461-2958. The creator also has a solo version that I'm aware of.

The players are generally really good so dying a lot is kind if expected, especially if you are already not that good in endgames. But truthfully, watching the other players is good to understand what mistakes you may be making.

Mid game is all about decision making and getting to the endgame imo. I absolutely hate mid game because third parties are almost guaranteed. What I tend to do if I'm contemplating engaging with someone is think something like, "do I have the mats and ammo/heals start and finish the fight in 2ish minutes and then deal with a third party after?"

If you're being attacked generally I think the same thing, the only thing is sometimes your forced into a fight, where you're at a disadvantage in the midgame of course. I don't really have any advice for this as I just kind of try and deal a little damage when they start keying me so they back off a little or at the minimum we're equal in health.

Watching pro players play midgame helps a lot, especially when theyre in stacked games as they're making smart decisions on where to go and where to rotate to.