Megaterrainish-type thing?

I'm about to start building a tactics/exploration game, and I've chosen large open terrains as my primary challenge. My goal is to create a ringworld roughly the size of the moon and make the entirety of its surface playable using terrain clipmaps and streaming (examples here and here). I could do this with a homegrown engine, of course, but I would really prefer to use Unity so I can take advantage of its other awesome features. :) Unfortunately, it looks like I'd have to get under the hood and tinker with some really low-level stuff in order to accomplish this. My question is:

Can I do any of this without a source code license?

No, you don't need a source-code license for that.