I'd suggest going straight for the bigger tank. You can always feed crickets in a tall, smooth sided bowl or tong-feed. It might be good to have a plastic bin with a ventilated lid or something to keep the frog while you clean the tank, though.

Most important things with these frogs is to make sure the temperature and humidity can be maintained in the tank. Also providing non-chlorinated water. (I don't suggest distilled for these amphibians though.)

All substrates have good and bad points. Changing coconut fiber/etc all the time can get expensive. Paper towels are pretty clean, but if you don't change them very frequently they grow bacteria easily. I went with the living tank: a drainage layer with a terrarium soil mix with live plants. That way the plants take up the ammonia created by the frogs and the soil never needs changing. Even that isn't perfect though, especially if you end up with some kind of parasite in the tank, it can multiply. That's what happened to me. Still, lots of people have had living tanks for years with no problems.

A few more considerations about this species: they can live into their twenties/ late teens. You might need to care for them for a while. They do call at night (to me it sounds like a distant dog bark.) You'll also need to make sure you have a reliable source of insects. These frogs seem to do well on nothing but crickets, but a calcium/multivitamin should help keep them healthy. It might not hurt to check and see if there's an exotic vet in your area, just in case.

That's about it, except for lighting. It's controversial because these are nocturnal animals but I've been linked a newer study which suggests it might help with bone density. Some lower wattage UVB light might help. I'd just make sure the frogs had a place to hide from the light if they want.

Also, yeah with a tank that size two frogs should fit. I have two frogs in the same sized tank.

I know this all probably sounds like a lot. But I think this covers the major stuff.