I know exactly what you mean about filling RAM. I lost a lot of work one day when I typed one character more than RAM would hold. The TRS-80 beeped and went immediately to the "I just started up" prompt. I had a cassette backup, but it was two-days old. Figuring out that I'd filled RAM was my first serious debugging session.
TRS-80 BASIC was my first language. The HS physics teacher (Hi Dr. J!) showed me the computer and handed me the manual. I worked on a program for a science fair project -- it translated simple English sentences into French.