Im running a vega rig and only run 3x vegas per gpu on 850W psus. If you plan to mod the cards to run @180W then you should be ok. My Vega 56s run around 220W mining without modding the cards using blockchain drivers. Personally id keep the 8gb RAM i had issues getting cards to mine at full speeds without it but others have managed it.

Celeron CPU works fine on for me but id agree if you can get an i3 or better for a few extra bucks i found it saves a fair bit of time resetting the miner and wattman when needed.

What kind of frame do you plan to use? My first one was a open DIY with good spacing but when i built one using a bought frame the cards run 20% hotter without some extra fans cos they are a bit closer together.