you can skip the 3060tis, it really isn't worth it. 50% higher hashrate, 50% higher power consumption and 50% more expensive than a 5600xt.
If you want to build a rig, look for cheap 5600xt (it is possible) or hunt for used ones
Your numbers are off.
my 5600ts do an average 44MH@95W, and my 3060ti does 60MH@140W. On amazon you can get the 5600xt for £280 and i got the 3060ti @ £430.
Numbers look pretty spot on to me
39 to 42 at 89 watts for my 5600xt's as cheap as 250 usd
60 to 62 at 140 watts for the 3060ti at 488 usd points to getting 5600xt
but I can not get the 5600xt for 250 usd like I did in october
https://www.bestbuy.com/site/xfx-amd-radeon-rx-5600-xt-raw-ii-pro-6gb-gddr6-pci-express-4-0-graphics-card/6398005.p?skuId=6398005
the one above is 330 x 1.07 x .87 = 308
so 488 compared to 308 is 1.58 to 1
62 to 39 = 1.58 to 1
basically a tie
if you have a 39th 5600 and get a 62 th 3060ti
it could vary but close to each one.
although an 8 card rig would be say 320 mh for the and and 480 mh for the nvidia
so space wise the nvidia makes sense.
RX 5700 XT is better than RX 5600
It used to be, but now that you can bios mod 5600xt, it is about 15-25% better than a bios modded 5700
an 8 card 3060ti would require a beefier powersupply or a second one. They are also hard to put in a compact space. Like you i have a space issue and have to stack server cases. It would stop looking for 5600xts once they come out with blower 3060ti