If you use  windows 10 and want to leave the miner to work long without reseting its safe to use 8gb(if you will get more then 2GPU for example 6-8) the price for additional 4gb is not a big deal here, the biggest prise is always the GPU cards( BTW the price went much lower cause of market capitalization went down)
If you were not seting up the rig before i can send you really nice free step by step guide i found when i was seting up my rigs, let me know if you need;)