Bigger problem is building over carpet. A sheet or two of plywood improves the problem.

I use solid core doors (have 3 at present), though I had a hollow core in the past. If you got room to work on both sides you can work on one assembly while another is drying. Same logic with 3 doors.

I don't use anything to pin into. I've never seen a really flat ceiling tile so I tape the plans in place, cover with wax paper taped down, and then tape parts to the table. Lots of weights and clamps help. The magnetic tables look really good, but something else usually collects my coin. A balsa bulding board sounds good. Who sells them?