They need land to burrow and breath. There honestly isn't a lot known about them but the assumption is if you want them to thrive they need the same requirements as the brackish fiddlers. I don't know what water parameters they actually need but assumption would be regular saltwater instead of brackish.
I personally never contacted anyone to ask where they collect these (would make things a whole lot easier), but I went through 200 species of fiddler crabs and couldn't find a match on the specific name. Quality marine list them as Paraleptuca crassipes (actually they list it as uca crassipes but that ain't a thing lol) but I'm not fully convinced (although their large distribution would check out), the blue ones I occasionally see look like Tubuca elegans to me, which is found on australian coast.
