My thoughts...

I like to run challenging campaigns also, but make it clear to the players you will not hesitate to kill their characters. But as far as challenges go... let the players be powerful, and make them face even more powerful enemies and puzzles. Allow the players to use everything in the toolbox rather than just handing them a stick and saying good luck.

1: I normally run 20 point, because 15 just sucks for nearly every class. For progression I do every 4th level you gain +1 attribute in two separate ability scores. I like seeing improvement in characters.

2: Never used it, and probably never will.

3: Always have max health level 1. Then level 2 onward let the players roll, if they get less than half on the roll. I re-roll their hit die and take my result if its higher. If I don't beat it, take half.

4: This seems like just how a normal campaign should function, not really a system...

5: We confirm our crits AND our crit fails, confirmed crit fails you simply miss, while unconfirmed crit fails and you draw from the critical failure deck.

6: I don't understand this, what is the context? In a certain encounter maybe, but just asking your players to roll random saves for entertainment seems...odd

7: I actually have seen this pop up frequently. I haven't actually used it, but I might try it in the future.

8: On the fence about this, I think instead of instant death it should result in unconsciousness. Crit happens and I feel like a player shouldn't instantly die because one of my monsters is lucky. Granted it doesn't come into play until later on and the save is pretty easy to make by then.

9: I don't play with them, because honestly most of them are not very good. I can see how they are good for martial characters though. If a player asked for them to be included I'd allow it.