You can develop on the original hardware, and I did a lot of work on my Jr
during the 8 years that I had it, but the floppy shuffle got very very old.
Back then I had a 256K system. After creating the requisite RAM disk to fill
the low memory hole left by the bass-ackwards video buffer there wasn't much
left. I was using the Zbasic 3 and 4 series compilers back then, and made
extensive use of overlays. (I wrote a BBS that ran on an XT for two years in
NYC.) If I really need to max out the memory I would cut the video buffer to
4k (text only), skip the RAM disk, and then have about 220K left.
I guess I'm spoiled now. My 'daily driver' Jr has 640K, full sized PC 5150
keyboard, DOS 5, an a SCSI drive (bi-di parallel port with a parallel-to-scsi
adapter). That's quite a better system than before and I wouldn't have to
shuffle anything, but my requirements have grown too. MASM 6.x might have a
chance of running on it, but Turbo C++ 3.0 won't, and most of the stuff
available from 1988 on up needs more horsepower than the Jr has.
Right next to it is the 386-40 with the much faster disk, networking to my other
machines for file transfer, etc. The 386-40 is there for data transfer anyway,
and it makes a good 'mothership' for the Jr. (It has a Central Point Option
Board, which is nice too.)