Help, multiple questions with collision and blender crashing.

Hello!
I made a character that dies and turns into a softbody, it collides with other objects from the character (weapon) and it just makes the game crash, so why? Is because my computer is weak? (2X512 GPU (Not a hardware expert here, is just what I could read out o the computer box)) Also I have been reading… Character type objects are a bad idea… Is there something more I’m not aware of? Why everyone online seem to dislike them? and what does exactly character motion does different to simple motion? It goes through walls too? lol

There’s some performance issues too which I fear, does any of the following takes out memory in big quantities or are bad ideas?

*Constant collision to trigger a character state (Think of it as when the character takes a lot of damage it triggers a trance which is just adding a cube over it so that the collision makes it go trance mode.)

*Picking up enemies deals a constant damage as the character is collisioning with it, but to avoid it dieing I just give it a health boost when carrying an enemy, this makes sometimes the character be unkilleable… Is there a way to be sure that the character health stays in reasonable ranges and doesn’t just go like -1000 and doesn’t die ever?
I thought of setting a margin, but not sure.

*Track to… Was… Well… My easy way to make a character follow the main character, but guess what… It is suddenly floating around the character spinning in circles but never collision with it…
It’s pet type character, but is suppose to collision with the main character and fuse, so you can summon it later, but if it never collisions, you can’t summon it again, I thought of putting it a “life” and if it doesn’t return, then it is kill and you can summon it after a time, but I feel that is cheating out my incompetency on programming…

*Running, I set forward arrow and a to run but it doesn’t move, i even tried putting it on two logic bricks and didn’t work either.
but a single logic brick (forward arrow) walks just fine.

*Going back to a previous level.
It restarts me the scene with all unkilled enemies, collectibles and at the start not at the door used to advance… I’m oing something wrong there I bet… What is it?

*Changing from one scene to another (menu) it should remove or suspend the first scene when doing this?
Also when changing from one world to another (not going back) it should be, load the new scene and remove the older scene?

Help… Please… Thanks…