If you are open to thoughts on the structure itself:
1 - Paint the posts & beams over the front porch white to match the soffit/gutters around the rest of the structure.
2 - I would be easier (and probably cheaper) to cover the exposed foundation area with white lattice than do the stonework.
3 - What is the overall feel or mood you are looking to create? Cute cottage, rustic hideaway (ignore my inputs on white paint & lattice), or funky artist residence?

If you can answer that last question it will help you design a garden that feels the way you want the guest house to feel. I hope this makes sense.

I'd give the edge of the porch the same treatment you gave to the front stoop and its steps. As to where to put the steps on the large porch, how do you want traffic to flow? Which directions are people likely to want to go from that porch?

You might consider installing railings where there are no steps, or at least where the ground is so much lower. You could also use landscaping to prevent people from falling off the edge, but landscaping might hide snakes.

What kind of clematis is it? The large-flowered kind, the fragrant Sweet Autumn, or the fragrance-less small-flowered native clematis, aka Virgin's Bower?

Is there enough light to grow grass? - your mock-up with the green on the ground looks good. If there's light enough for grass, I'd be inclined to just use grass, with packed gravel paths, and ornamental small trees or shrubs that can be limbed up to keep the ground clear. I'd add interest by paying attention to the shape of the lawn and paths so they are interesting features on their own. If grass doesn't grow, maybe using different textures/colors of packed gravel and flat rocks could be used as a substitute...? [Although I don't like some of the features in ideasshare' mock-up, I think she might be in the right ballpark here...] But since snakes like to warm themselves on rocks (or at least the ones I knew did...) you'd have to think about that too and avoid making resting places for them - at least where they'd be hidden from view and could be startled. A tricky landscaping probeim indeed...!

Since I spent a fair bit of time this spring and early summer trying to find the 'sight' greens to paint our shed, I'm interested in what your solution was - so I'd love to see your chicken coop :-) You can see our green solution in the link below - skip to the botttom to ignore all the agnst of the selection process :-) We're quite happy with it and I think your shed/guest house would look great green.

I've been thinking more about the snake problem (which creeps me out a lot! :-) I think you need to check on what sort of conditions the snakes you are dealing with like for nesting and winter hibernation. I'm concerend that walling in that under-space with rocks might make a perfect cozy nesting site for them! Although I don't know specifically what they like or need, the thought occurs to me that maybe what would deter them is to fill all that enpty space with a sharp gravel, well rammed in; then surround it with panels of fine mesh in a strong material with the top attached to the structre and the bottom buried down a foot or so. Then compact the ground and build the decorative dry stacked stone wall. But you'd have to check with a snake expert if that would work.

But seriously, I did have a thought. Are there any natural snake predators in your area? If so ... is there anything else they like to eat that you can plant near the guest house to encourage the predators to frequent the area? We don't have snakes, except for garter snakes, so I don't know what kills them aside from mongooses and they also kill chickens so they aren't a good solution (and they live in the desert).

Is Mountain Laurel native to your area? For a pretty woodland look it is really attractive in the spring, I've been coveting it lately & the shaggy look would be casual in this garden.