I would like to create a web service to support installations of our main application in the field and handle things like logging errors, providing version notification, updates, activation keys, etc.

A single general purpose application that accepts encrypted messages and distributes tasks seems easier to maintain than several. Since it doesn't have to be up absolutely 100% of the time, it can be stopped for updates.

I need guidance on how to go about it from the ground up.

TIA,

Alex