It's possible to mix AMD and Nvidia cards on the same mobo, but it tends to be temperamental and not really advisable for the noob miner.

I have a dual GTX 1060 3GB rig mining ZEN that delivers about 610 H/s on average and uses a total of 315W at the wall (the entire system). Cards are set for 85% power limit and modestly overclocked to 2000/4150.

If you mine a Cryptonote coin like Monero, Electroneum, etc., then a powerful CPU can easily pull its weight. The Ryzen 5 1600 I have in one desktop does 370 H/s while an older FX-8300 still delivers a respectable 190 H/s; a really ancient Phenom II 955, however, only manages 55 H/s and Windows (7) slows to a crawl.

So a possible setup would be two RX 570 or GTX 1060 plus a decent CPU so you can use a GPU miner program at the same time as a CPU Cryptonote miner (e.g. - Claymore's v3.9).