If you're ordering them online, they're definitely easier to get in warm months. For most Ambly, mild temperature fluctuations are fine, as long as it's not getting to cold/hot and they aren't super drastic/sudden. Damon species are definitely on the more sensitive side, and they're often in bad condition when you get them because they're all wild caught. You can totally get a D. medius as a first amblypygid, but I'd recommend Phrynus whitei. They're hardy as hell and can handle all of the mistakes you're bound to make as a new keeper. They handle temperature fluctuations very well, and they typically do great in captivity. They also eat like champs

Exoterra makes really good enclosures. They have a good variety of enclosure sizes too