I didn't think "overfilling" it would hurt the engine. I'm just wondering if there's a correlation to this smoking-not-starting issue and the fact that I filled the tank more than usual.

As for 1/3 capacity question-- basically I'm trying to say that the bottle seems to stay at 1/3 capacity. If I fill it with more, it'll be back down to 1/3 the next time I check it. However, I've not seen it go lower than this.

Windshield greasy? No. Are you thinking of gas vapors from the filler? I've had my filler refurbished somewhat recently (well after any issues here) and I know it's not a perfect seal but I think it's OK. I have a locking gas cap that I will replace with the standard DeLorean non-locking and better-sealing at some point soon too.