You lucky,i wish i had rtx cards
If you are going to with 2 rigs then i would pick:
mobo: gigabyte h110-d3a(6GPUS), biostar b250 btc, these are cheapest and not bad. asus b250 mining expert,
Cpu : g3900,3920,3930 or pentium g4400, what you can fine  cheap
RAM : 8G
SSD : 120G
PSU for 4 3080 minimum 1200w,recomended get 1600w like seasonic but they are very expensive. get 2 1600w psu good one. dont forget running them undervoleted or power limit then you will be fine.

For beginner just start with hiveos or nicehash. maybe nicehash will be more easy for start. you just need install windows and download nicehash.