Strings with maximum length are a bummer but null terminated strings have their own problems and are part of the whole "unsafe at any speed" nature of C.
The thing about the CoCo was that Radio Shack sold an absurd number of peripherals for it.
I got a "multi-pak" which would let me plug in four devices to the cartridge slot and I had a real UART for it. The built-in sound was awful but you could get an Orchestra-90, a speech synthesizer cartridge, etc. Most of the hardware and software at the time supported hardware flow control which made the bit-banger serial report more reliable than you might think at low speeds.
The video was a real problem, I think a lot of software didn't get ported to the Coco because everybody thought 40 column text was bad enough, who wants to deal with 32? For instance I never saw the Infocom games being available for the Coco although I found out just recently that Infocam had made a Z-Machine interpreter for it. Eventually they came out with a Coco 3 that had 80 column text and high resolution modes with a lot of colors but it was getting late at that point.