(1) do you think Apple will reduce the number of ports? Particularly get rid of USB-A, 3.5mm headphone jack, and SD card slot?
I don't think anybody would be surprised if the new iMacs are USB-C/USB4/Thunderbolt 4 only. However, a couple of counter-points to ponder:
1. There might well be two versions of the new iMac - with a 21.5" replacement Real Soon Now using first generation, low-power Apple Silicon, followed later by a "pro" range that replaces the 5k and, possibly, the iMac Pro, using some sort of "Apple Silicon Pro" (which could be anything from a Fantasy Xeon Killer to a slightly higher-binned A14Z). Plenty of speculation on this elsewhere. Also, we know nothing about how PCIe and Thunderbolt/USB4 are going to be implemented on Apple Silicon, and that could have a big influence of what port combos are possible.
2. Apple dropped everything but USB-C from its Macbook Pro range 4 years ago (and it didn't waver with the 16" MBP that backtracked on some other issues). However since then, the iMac got updated to Thunderbolt 3/USB-C
without losing its other ports, and they've radically updated the Mac Mini and Mac Pro and
kept USB-A ports, ethernet ports and (on the Mac Mini, at least) the headphone jack. So there's some hope (I suspect SD card is for the chop, though).
Thanks all for your input. If they release the new models and they're not to my liking, will I be able to pick up one of the current models at a decent price? Perhaps refurbished?
Well, the price/availability of end-of-line/refurb/used Intel Macs is going to depend on the initial success of Apple Silicon Macs - if they're a hit, the market will be flooded with refurb/unsold/Intel Macs. If there are major teething troubles and lots of people don't like the new Macs, the remaining Intel models could be like hen's teeth. Nobody Knows.
However, I wouldn't be surprised if Apple keeps one or two Intel models on the books for a year or two - look at how long the non-retina 13" MacBook Pro and the classic MacBook Air hung around.