"Is it practical to run VTP on just two switches?"
Depends what you mean by practical. For just two switches, not a whole lot of "need" for VTP.
"One as a master and one as a client? Or does it make more sense to just have them both as a master?"
What version(s) of VTP do you have in mind?
"Is VTP only required configuration supporting more than two switches?"
It's never required, just that its purpose is to ease VLAN management, when you have the same VLAN(s) on many switches.
@Flavio Miranda notes VTP as being useless although further noting having never seen it used in even a single environment. I, though, have seen in used, and used it, it a couple of large Enterprise environments, and personally, I liked using it.
Flavio also mentions using it, damage can be catastrophic. There he's correct, if using VTP versions 1 or 2. I've seen it happen in a large scale Enterprise environment, using versions 1/2, because those versions don't preclude, by default, stupid mistakes using VTP. (Sort of like early DOS which didn't ask for any "are you sure" confirmation when you typed "format" while the hard drive, C:, was the current drive.) VTP, version 3, though, makes it much, much harder to make stupid mistakes. BTW, versions 1 and 2 can also be configured such that you have to "work harder" to make stupid mistakes. It also helps, to understand how VTP actually works, like for instance, for VTP versions 1 or 2 the true meanings of "server" vs. "client".
BTW, version 3, never much caught on, one possible reason being, with L3 switches, and/or large port hosting switches, often resulted in many fewer switches that would be within the same VTP domain. For example, I've had used a 6513 with eleven 96 port cards, i.e. just one place to define VLANs, vs. using 44 24 port switches to provide the same edge port count. The latter, if you had such, is where VTP seems to have benefit.
