the end position in post #21: can Black just play Nxe4 now?
Defensive openings for white

Well, I'd suggest the Barcza-g3,Bg2,Nf3,0-0 and follow it up with d3(KIA). Your opponent will have problems facing you.

Just to throw in my two cents, i find myself to play better as black as well. I think what you're looking for is the difference between initiative and reaction. White, obviosuly by going first, has the initiative, and black is forced to respond, having the reaction.
As white, I tend to play the Zuckertort, mainly because it gives up this initiative and leaves black in the dark as to what defense to adopt. This reverses the roles, and seeing as the Zuckertort is transpositional, you can react accordingly to their move. You can easily go into more aggressive openings, like the Colle or English, or even look at trying some reversed openings.
I agree with Eric here, I ALWAYS use the Colle and if my opponent makes just one mistake, I get a middle game ending quite well for me, and a very protected king. Although this works well against skilled opponents also, making it hard for them to get to your king, and harder to break through your defence.
I actually generally use the Colle as white, and as black, I use the Colle if my opponent starts with anything apart from king pawn to d4. If they start with that, then I use the bishops opening, because it can lead to scholars mate if your opponent doesnt suspect it, and it can also lead to lots of both offencive and defencive set ups. Honestly, I dont know many openings but I find I always have good games as white with the Colle, and black.

Am I reading correctly that defensive openings for white are closed positions?
Can come in to play when facing the Petrov.
If you do not take advantage of your first move to grab some center and rough up Black, he will take the initiative and start slapping you around. With better skill and understanding, you can start to be more aggressive in the opening and have some fun with White.