Questions regarding a small mining farm.

20 x GTX 1660

Greetings! I've come across this seller claiming to be a wholesaler selling used gaming products. He is ready to sell the cards to me at a tad bit lesser than the msrp. I would be able to check if each ever card is working and he claims they have manufacturers warranty. My questions- Is it worth it?(I've been mining rvn with my 3060 in my gaming rig.)Wouldnt 20 x 1660 require atleast 2500w psu(s)? How would i connect them; should i buy a single motherboard with 20 pcie connectors or does it not matter? Would performance decrease if i use risers? Would i have to use a linux mining distro to recognise all the cards or will windows do that?( ive heard windows has trouble recognising multiple cards). What are the best oc settings for rvn? Thank you for your help!

edit : I have done a bit of research and I've answered most of my questions but i wanted to know other people's opinion on it. Like, for say i already have 3 spare motherboards(w/ cpus) with me that has a total of 10 pcie connectors. I'm thinking of getting 3 or more second hand motherboards. as for the psu i im getting 5 psu with 4 x 8 pins( not sure if this is the best option as there'd be a a lot of unused capacity; need help on this). For the os, hive os and minertstat os seems like a good option but the 3$ per rig makes it an unattractive offer(wanted to know if there were any alternatives). I read x16 risers only make negligible difference. thats about everything i've found. please correct me im wrong anywhere. Is there anything i've missed out?