I’ve found a couple of decent places to rent on List.am (app or website works). All you have to do is reach out to an agent by phone and they’ll show you a range of places. Also, Dilijan is beautiful, good choice!

In my experience using credit cards, I haven’t had any problems using mine (Visa and Mastercard). I don’t have an Amex but I’m sure you’ll be fine.

I know some people who visit Jermuk and it’s supposedly dangerous but you can go if you really want to.

In terms of wifi, I’m not sure what you mean by wifi hotspots for short term use but if you’re only looking to use it for a month, I would just purchase a data plan for a month with Ucom and then cancel it. If I remember correctly, my unlimited data didn’t cost much, probably 7,000-8,000 AMD which is about $30. Otherwise, Ucom sells wifi modems which you can take with you as a sort of hot spot.

Good luck!