Hmm, interesting. About SHH ED, though, it's only Wordstar-like in the interface (or so I'm told;) it edits plain text quite nicely (except that it chokes on tabs and just displays the corresponding CGA character, don't ask me why.) The main reason I'm using it is because it's small and fast, which is a major asset on smaller, older machines, but doesn't impose any kind of artificial restrictions on file size. Problem is, a lot of these newer editors focus more on being feature-rich, which is nice if you're not trying to load the program from an old, slow hard drive on a 5-12MHz machine :/
Update:
Sam's Little text EDitor (SLED) is also 17KB, and while it's still not quite as user-friendly/familiar as EDIT (mostly in the block-manipulation-type commands,) it's a lot more straightforward than SHH ED, and still has no size limit except conventional memory.
As for assemblers, Robert Östling's
MSA seems like a good choice, since it's ~28KB and real-mode compatible. It's apparently mostly NASM-compatible but missing 32-bit compatibility and all output formats but COM, but that's no great loss for my purposes. Think that's what I'll be going with
GASM is fully NASM-compatible and <100KB, which is cool, but it's a protected-mode application :/