In this image (from sevenless's guide), can I walk on the "untiled" spaces between the paved squares for the trees, or will that stunt them? If it does stunt them, what is the point of the tiling? just aesthetics?
The only time stunting will happen is if a tree tries to grow the exact moment you're in the radius. The odds of that happening are pretty slim.
That said, those untiled spaces aren't "safe" to walk in. They're within the radius. It's mostly aesthetics I guess. I've seen other variations as well.
It really depends on the tree. Some trees can be planted closer together. What is pictured is considered the standard 'safe' distance. Stick to it unless you're willing to experiment yourself and not get upset at bad results.
Opinions expressed in this statement are the authors alone and in no way reflect on the game development values of the actual developers.
More or less, yes. I think Loftar once said that the actual spacing needed depends on the size of the tree's graphic... so it's not as simple as squares. You might be able to get away with closer spacing with mulberry trees, for example, because they are small. Most people just go with what you see in the image, though, because nobody wants to wait 3+ days (or many more) to find out if their plan is junk or not. I would recommend sticking to what you see in the picture too. =)