Oh I see.... My bad.
You said: "How much frogs would fit comfortably in a 60-gallon?
It's not really deep, but rather long and tall." and I thought you meant you intended to turn it on end, silly me.
It's not an enormous tank but yes it should be fine if set up in it's intended position.
You don't seem to be set on one type of animal yet, so yeah you need to decide for yourself. Don't choose frogs if you want to handle your pet. Frogs breathe and drink through thier skin and even residual hand cream / perfume would be deadly to most frogs. Even the natural oils on our skin harm them.
When you decide what herp is best for you then you'd build the habitat in the there specifically for that animal. I'd suggest building the habitat first and then brining the animal home and not the other way round.
Post build pics!