Garage layout.

Congrats on your first home, sure looks nice.  It would be helpful if you could post a diagram of the space.

Nice house, and congrats. Wishing you and your wife, many happy days.

As for a garage layout. I installed walls and a ceiling for my train room in my garage many years ago and don't regret doing it. The other half of my garage houses my wood working shop.

Although my wife complains now and then that her car, along with mine, parked outside, needs to have a "covered house in the winter". But she's happy when I make new cabinets for us or one of our kids, or making a toy box for the grand kids.

My layout room is 9 by 12 and started out as a very nice scale HO layout. A couple of years ago, I moved up to O gauge, 3 rail. The new configure is not as elaborate as the HO, but is very enjoyable especially when the grand kids come over. 

I belong to a local club, so that I can run my large engines and longer string of cars. 

Enjoy your garage layout.

Ray

I think your idea of the wall is a good one and I would also insulate it. It will surely help with temp control and utility bills as well as dust/dirt etc. as in keeping the layout cleaner. I would say the heating and a/c would be a must (for me anyway) for year round train operations. I would also make sure the existing walls and ceiling are insulated to what ever is required for your area, same for new wall.

Something like the Mitsubishi Split Systems would be a good choice for heating and cooling the space for your layout. Mitsubishi is the only one of this type I have seen in person, there are many other brands available for this type of system. Find a reputable dealer that knows how to properly install these type of systems and go from there. A lot depends on a quality installation from a dealer that knows what they are doing. This is probably more important than brand names. Of course a knowledgeable/reputable dealer will probably also be selling a good quality brand anyway. (Sizing is important! And they should do a load calculation for proper sizing. Important for both utility bills and comfort!!)

Looks to me like you have a great space that can be made to work well for a layout. Also a very nice looking home to go with it! Congratulations and I hope all goes well for you and the layout.