Kind of a lot to address here so I will summarize a bit.
Build the machine to suit your main purpose, Flight Test Planes? Balsa is no problem as well. This is the first little snag Carbon Fiber. CF is easy to mill but dangerous and should always be done wet, also it is stupid expensive to get sheets of it. Full quad frames including hardware and shipping are usually cheaper, even armatans.
You don’t not have to use the dual endstops, most of us don’t. It is just and option to really increase usability for advanced things like tool changes, and really precision sensitive parts. If you get a Rambo board you can always add it later.
Options here as well, laptop is fine, an LCD is super convenient, or a pi running octoprint.
I guess what I am getting at is there is nothing set in stone. There is a bunch to learn, starting with the foam core planes should be super fun and a very easy way to get some machining time under your belt.