11x11 new layout

Do you have a track plan to share?  My 2 cents but forget about the longer screws.  I suspect you are building this in a spare bedroom given the size of the layout.  Attaching the track to the wood framing will create a remarkable amount of noise that may "issues" with others in the household.  Track needs to be secured but not as much as you think.

They are in the hardware isle in brass, packages of 100 at the Depot. Crown makes them.

If you plan to paint your foam surface in an earth tone as many do, remove the poly skin first so the latex paint will adhere better.

Also, track screws can be removed after glue-ballasting the track. You can fill the screw holes and color the repaired tie face with black/brown Sharpies.

Just as a suggestion, if you do decide to remove screws later it is easy to find pan head or round head screws that do not have the shoulder that a standard flat head wood screw has, normally requiring a countersink prep to avoid splitting.

Wood tie Gargraves Flextrack shown in photo below.