Questions regarding space in the middlegame

At the present time I am studying a middlegame book and I have changed the way I play somewhat, trying to incorporate some of the strategies into my game plan.  Unfortunately for me things are not going as well as I had hoped and would like to ask for some advice/tips on this subject.

I have hit a tactical/calculation slump lately for reasons I cannot explain, but I am working on that.  This is the major cause for most of my losses lately, but I cannot help but feel that I am placing myself in an inferior position early on (because I am still misunderstanding some early middlegame concepts), which is troublesome.

Here are some annotated examples and questions I have.  Thank you in advance everyone!

Apart from my awful blunder, was my understanding of the middlegame correct?

Don't move too much pawn in the opening. Because a pawn move (expect central pawn) removes a tempo per develop a piece and you can be simply counterattacking if you play too aggressively

Thank you so much once again for your insights Paul!

In the third game you had 7. dxe5 wining a pawn, Black is too under devolped to do anything about it.

In the second game I would have played 6.Bd3, followed by Nge2 and O-O. I anticipate that Black will completly close the center with e5 and d6. I would then be ready to strike with f4 and maybe a latter e5. That way I wind up with more kingside space and better devolpment. I played Bb3 first because in the Modern Benomi structures, what you get if Black plays exd5 and you responded with cxd5, the knight belongs on f3 in order to support an e5 break.

GRRRR!   Thank you aggressivesociopath!  Gosh, it is indeed frustrating for me to discover these "obvious" tactics after the game...   I have a long way to go still. *sigh*

Hello,

     I don't have the time right now to look at your games.

I have to go give an estimate on a paint job.  I have not worked for some time now because of the nerve damage to my foot  Need to try to get back in the flow...

     I'll take a look at your games when I have time.

Peace be yours - DJGianatassio