Speaking of tools, your hollow-core door is also a tool. Don't presume that it's flat. Measure it with a straightedge or a taut length of string. Ensure that it's flat on the length, width, and diagonal (i.e., ensure that the door isn't warped.

Another thing to do is to take your original plans and have them copied. Keep the originals safe in case you need to refer to them again. Use the copies to build from, and you don't care if they get chopped up with the ol' X-Acto or not.

Also, if you happen to do some covering, save the backing off of the Monokote to put over the plans where you intend to glue. Most (but not all) glues won't stick to it.

Also, I have to agree with tools that these other guys have suggested. Stay away from the 'trick' tools and ask the guys at the field before you buy one. I've got tons of tools that I don't use.

As you get into it (and you decide that you're going to build more kits) you can add things like an inexpensive sander and benchtop jigsaw, but you won't use them on your first couple of kits.. only those that you wind up kitbashing.

Just my $.02. Like everyone else says, keep it simple. You'll be surprised at how few tools you actually need, as long as you get good ones. And, don't be cheap on the X-Acto blades.... Don't ask me how I know that...

Bob