1) Complex system that would make it a bit more difficult to roll a joint -> No, it is too much a RPGish system. I don't really like the idea, plus imagine if you're roleplaying and you have to roll a joint and people around you has to wait you to finish your "mini-game".
2) If you got pot you would need to grind it first -> Same, too RPGish, plus the grinder would be useful just for this thing, seems to be a useless thing that might be role-played.
3) To me tobacco can be added and mixed, for this thing is a yes.
For the rest mmmh.. I am not sure, I mean.. this is that kind of things that might come with you as long as you're roleplaying.. I mean, if I buy a gram of marijuana I am not just going to fire it up and smoke it, I would roleplay something before for obvious reasons.