I've never used them but it's what I would use for a cage of that size, especially if you're making one single unit with multiple cages and a snake that will climb. You don't mention what material you will be using but heat tape doesn't work very well (if at all) with wood enclosures, but will work with plastic if you go that route. I will defer to others on the exact size, but I would say you'll need at least 120 watts, if not 160. Plus a t-stat.
RBI Radiant Heat Panels