Dealing with flexible opening positions For some reason I feel uncomfortable in positions where the opponent has not committed any of his pawns in the center and was wondering why is that? I guess it feels like I'm not sure how to carry on in positions such as those. Here is an example of what I'm talking about.

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq -"]
1.g3 e5 Bg2 d5 Nf3 e4 Nd4 c5 Nb3


I also tend to be very concerned about pawn breaks and my opponent using flank pawns or something else to attacking my center. Is this fear a valid one? Such as if lets say as a continuation from the previous example

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq -"]
1.g3 e5 Bg2 d5 Nf3 e4 Nd4 c5 Nb3 Nf6 d3


Something like d3 in those situations really bother me for some strange reason. Like I want to keep my pawns intact and so on. I have a feeling that paranoia such as that may have an impact on my thought process and then game.
As a general principle, when my opponent is breaking (in a loose sense) the opening principles by not occupying the center, I try to combat this by following the principles even more. As a result, I would try to avoid making multiple pawn moves and instead try to get my pieces out once establishing e5 and d5. 

For example, in your line I would play something like 1. g3 e5 2. Bg2 d5 3. Nf3 Nc6, defending the pawn and getting started on your own development. It's worth noting that while 3...e4 looks good because it seems to gain a tempo on the knight it also cost you a move to make, allows your opponent's bishop to be opened up (the pawns probably won't last long as they are) and you're committed to d5/e4 instead of retaining the flexibility of being able to make either pawn move in response to what your opponent is doing. 

I guess you could argue that 3...Bd6 is also an option as it allows c5 soon, but it also removes a defender of d5 and goes against the advice of developing knights before bishops. Nc6 looks good to me and I'd just keep moving pieces to useful squares and see what kind of setup white ends up going with before making too many more pawn moves.