Looking for suggestions on adding levels to first layout

Dang, you've got plenty going on already!! Great job for being a beginner!

Bob- welcome to the forum. That looks like a nice layout for little ones to play with. Scenery is an open book. You can be as detailed or simple as you like. Tunnels are easily made with the same rigid foam you are using for the baseboard. It can be layered and carved as you like and painted with cheap acrylics. Several guys use a woven cardboard structure and plaster cloth to cover.
This is a before and after of a corner I did with foam.

Bob

Thank you Carey.

Bob, I'd like to keep the board relatively lightweight so i like the idea of using the foam. 1) What is the best way to carve it without making a huge mess or destroying it?

Also, my two loops will go through the tunnel (with minimal space between them but enough to have 2 trains safely pass each other). A few more questions.... a) Would you put a middle support of some sort between the tracks in the tunnel? b) Is the foam sturdy enough to support the train overhead c) what do you use over top the sides of the tunnel (wood, cardboard, another piece of foam) to enclose it?

I really appreciate your comments and especially the pictures. Curious, how did you make the stone sides on your tunnel? Thanks,

Bob

You can raise track sections and and create uneven terrain by carving 1" or 2" foam into small up and down ramps. In addition, Woodland Scenics makes foam risers that do the same thing, although I'm not sure you need or even have enough room to do that.

If you can start your graduated trestles back closer to the switch, you may be able to gain enough height to install a bridge along the long side wall. The Lionel bridge with flasher (6-12772) and rock piers would be a good choice and add lot of visual interest if you can fit it in. You might need to swap the trestles from the Lionel set to the MTH set.

Thanks,Richie!

Bob, Here is what I have been doing.  I purchased the Woodland Scenics foam product for my grades.  I goofed in where I started the grades, so I added another layer of foam to one of the grades.  It is sturdy enough to support my heaviest train.  I also have a grade in the front where I want to see through to the town and trains behind it.  I used a trestle set much like you have.  It is solid too.  Someday I want to change it out for something better looking in my opinion, but who knows when that may be.  If you put a support between tracks, make sure you have plenty of clearance for trains on the lower level.  Maybe you don't need it if it is solid enough.

I have used foam for scenery base like Bob showed, and I plan to do it again on this layout.  You can cut it with a serrated knife, some folks use a Stanley Sure Form rasp tool.  You will have a lot of crumbs to sweep up.  Others use hot knife tools, but you have to ventilate for fumes.

Bob

If you use Woodland Scenics inclines you'll need to double up. The WS risers (2.5" wide) are intended for HO and N. Since Lionel Fast Trak has built in roadbed, the WS inclines would be too narrow. You could also use single inclines and build them out with cut foam sheets. I chose to double even though using Atlas track. Having built in roadbed, you wouldn't need a plywood sub-roadbed, as I have.

Thanks, Oman.

Thank you, Mark. The pictures are very helpful.

I have built free standing inclined subroadbed ramps and upper level roadbeds out of  thin 5.5mm Meranti plywood and made tapered rising walls out of bendable plywood which can conform to any curve(s).

Very light weight but you can stand any where on the incline section.  Lots of rigid structural integrity and can be lifted up at will without flexing.  One 4X8 sheet of Meranti and one 4X8 sheet of bendable plywood would more than do the track pan shown in the photos.

Additionally, using the bendable plywood to form the ramp profile allows you to gently form the vertical curves at the bottom and top of the ramp.  Real slick finished product, no abrupt vertical angles.

It is not necessarily the thickness of the plywood but more so the construction techniques used that develops the strength and rigidity.