Your judgement so far is excellent good kit choice and good start on the tool set.

Let me start with the last item the building board: I built airplanes under contract for years on ceiling tile (mounted to a FLAT door). Homasote and balsa are both a tiny bit better than ceiling tile but, believe me, the difference is way too small to talk about, and at two bucks for a 48" tile, you really can't go wrong!

On the bar sander, the 11" jobs have been a good bit more useful for me than the longer ones I use a few 11-inchers mounted respectively with fine, medium, and coarse "sandpaper." They are way more useful than I expected before I got to own and use them.

Something I'd recommend is a razor knife. Zona is famous for them; I think SIG has them; I used an Atlas one for years (the Atlas one made for model trains and available for about $2). Great for smooth, precise cutoffs, especially cross-grain.

Clothes pins are good clamps for low force uses, and they only take a couple seconds to customize for higher force, longer reach, special clamping angles, etc. Some dollar stores have those and little (like 2") spring clamps that are good when a little more force is needed. Of course, there's also an endless variety of things you can do with rubber bands, popsicle sticks, and paper clips.

I found that a good covering iron was well worth the cost for me. I'll spare you my misadventures with the less expensive ones, but I will tell you that I like a good bargain and I now use a rounded edge, 2 degree temperature controlled iron at certainly 2 or 3 times the cost of my first ironS and I consider it a very good deal.

Think about wood glue. (My personal favorite is Titebond II, but there are a variety of good choices.) When an assembly is pinned to the table, slow drying time (my choice sets in 20 minutes) doesn't slow you down a bit but in the end, you get a more flexible (harder to shatter) joint, more working time (to fine tune part alignment before it's too late), no fumes or toxins (check out the hazard reports on CA, Urethanes, and epoxies), and lowest price of any of the popular kinds of glue.

So, that's a start I know there are a lot more ideas out there.
Good luck, but mostly building is a great and satisfying enterprise ENJOY!