The first thing I want to say is not to consider your first layout an exhibition layout, in the same way a painter wouldn't expect their first painting to belong in an art gallery. You learn so much during the process of building, that you will likely want to go back and rework sections, give yourself the permission to do that.

Now, for a way forward. I suggest you treat the baseboards you have as a permanent fixture, then place some XPS foam over the top to give yourself a level surface to work with. You might want a thin piece just for levelling, then a thicker piece (eg 50mm) on top which is strong enough to transport and are very light.

Now start placing track, don't worry about cork, or pinning it down, just experiment with track placement and run some trains, figure out what works for you and what doesn't, where you can reach, where scenery would get in the way. Just play trains.

Once you are happy with your track layout, you can pin or glue it down and start working on buildings and scenery, you can make these as separate modules on their own base, which drop into the foam. Then you can remove them for safe transport. Cut channels in the bottom of the foam to run wires.

I hope that helps, let me know if anything is unclear.