New to mining, have a few questions

Hello

I recently started reasearching about ethereum. Id love to start mining since I already fold on my GTX 970 and getting an additional card to make up for the power bill would be great ( and earn a couple bucks in the procsess ).
My questions are :

Can I get another gpu to mine Etherium alongside my gtx 970 which is used for folding and gaming? It purpuse would be only mining 24/7.

I can get the 390x for around 200 eur used, same for 390 and the rx 480. Which one is the best? ( My KW/h is pretty low about 0.07 ish) I guess the best would be the 390x but i would have to upgrade my psu ( I have a LC-POWER 650w which probably wont be handeling two maxed gpus 24/7).

Are those etherium calculators accurate ( im looking at he crypto compare one). With both the gpus running (only the 390x mining) I would still have 90 eur profit per month??

With the whole system, the 390x mining at 32mh/s and gtx 970 folding, Im looking around 700w of consumption so a 850w should do fine?


Thank you alot for the anwsers and sorry for any mistakes in spelling.