9) I suppose you mean the Invincibility carrot. It's event 88 and so it's spawned by MCE's with their event parameter set to 88. In fact you don't need an MCE to spawn it in MP though. However, for reasons I don't know, in MP this pickup is fully blocked by JJ2+. I've heard about a bug related to Invincibility carrots but I couldn't find even a single note about it's removal in the Plus readme and I don't think any other event was removed like that, without any possibility of spawning it, so this may be unintended. Later I might do some research on which version of Plus removes it and what can it be related to but I don't really want to promise anything.

Could you explain points 1 and 7 further? I'm not sure what do you mean by "wires", perhaps some hints on how did they look like? And I have no idea what is point 7 about, probably something related to dying in Save & Run mode, but what do you want to achieve?

Edit: Oh, and I've just found a foolproof way to get a flying spring. Place any (vertical) spring (I think that parameters don't matter as long as Ceiling=0, obviously) on the floor, then place any PU (excluding TNT), any working shield, a Jazz-Spaz Morph, a Bird Morph or a Trigger Crate above it. Then it is important that the pickup object spawns first, so you have to approach the area from above and only in SP. The springs will fly away as you get close. No other container-type objects seem to work so I suppose it has to do with the size of their sprite. Other than that I have no idea what makes it work.