ThunderBolt Macs can get up to nominal 2500 M Bytes/sec on an appropriately fast SSD drive in a ThunderBolt-3 enclosure.
if you don't do any of these:
edit Videos, add special effects
produce magazine-cover graphics daily
simulate weather
simulate nuclear explosions
do airframe stress calculations
use custom PCIe slot devices not available as Thunderbolt devices
... you likely don't need anything more than a MacBook Pro, or possibly a Mac mini. If you want to go completely crazy, you could buy a Mac Studio.
Unless you need to use drives that requires transfer speeds in excess of 2,500 M Bytes/sec (ability of thunderBolt enclosure) or have custom Hardware to plug into a PCIe slot, you certainly don't need the newest Mac Pro.
As for upgrading memory, you can't. The BIG architectural 'trick' with the M1 & M2 Macs is that the memory and processor and screen I/O and misc I/O are all tied together at memory speeds, and it performs because you NEVER copy stuff around, you just pass a pointer in the only memory array there is.
I own three of the Mac Pro 2009 version. This transition period is very difficult for me as well. But I can not justify the costs when FAR simpler hardware just over 'entry' level does everything I ever wanted to do and more.
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Just specify more than you think you will need, because there is no "mid-life upgrade" possible now.
