Welcome to the Netduino community. Let me see if I can answer a few question for you here...
Yes, Netduino Plus is probably the best value. Netduino Go is the high-end board with the most capabilities (including support for go!modules like the Nwazet Touch Display Module). Netduino Go is very new so a few features of Netduino Plus are coming but not quite here yet. All of those will fill in over the summer.
That's a good recommendation There's a starter kit for Netduino Plus planned for late summer, but today most of them include the basic Netduino. That said...it's pretty straightforward to pick up each of the starter kit parts.
Thank you Chris for the speedy reply and detailed explanation. It sounds like the decision to start with Netduino Plus over Go, or vice-versa, is an important one as they really are separate products with separate purposes. It sounds like, and correct me if I'm wrong, that Plus takes advantage of the compatibility of Arduino, which makes it flexible, while the Go takes advantage of a modular architecture, which makes it easy to use. The Go would probably not be compatible with sensors, shields, etc. from other architectures, if I understand correctly.