If only for mining maybe its a good choice but if you want only use that for mining you need to mine another coin eth is more for rigs mine some cryptonight coin with that you can include cpu too efficiently but make sure find coin with small diff

From them sata connectors risers take more then 75 watts and sata is rated 50 thats how you burn youre shit

yes because of the DAG file

Well if those things doesnt matter for you theres no problem just dont use sata adapters that are included with risers and you will be good to go

Its better getting few 1600 watt then alot of 600 watt psu looks cleaner less sockets used and dont forget to buy minimum bronze rating