Figure out how many vendors you're going to have then try to arrange them how you would like, and plan your deco around them. Unless it's just a few vendors (5 or less) then you can usually do deco first and plop vendors down later.
I like to display wares I am selling in front of the vendor. But that's mainly because I have 10000000 vendors, and even with displays out people still ask me where stuff is. (Hi my name is Sarah, and I'm a vendor addict.)
Depending on where the road is in orientation to your house, might affect where you stick your vendors. - if its to the west then you'll want to put them out on that patio area, or if its closer to the front door then stick them on the porch. The roof is also good. You'll get more traffic with visible vendors than those inside the house.
Moonglow is lovely, but it really doesn't get too much traffic in general. So drop a lot of runes regularly, and put shop runes on one or all of your vendors. You may also want to look at marking a small rune library (t map is good), or orienting your shop around a particular clientele. Like you could specialize in items to help the new player get going (cheap 100% LRC suits, -29 spell channeling wands, cheap armor with good phys resist, etc) then name your shop "the new player haven" or something similar.
It really depends on what you're going to sell. If you want to make money then you'll probably go in a different direction (like champ spawn replicas or doom arties), however the more pricey an item is the more it will cost you in vendor fees over time, which is why rune dropping and gating at prime time hours becomes crucial.
Large marbles are beautiful, but marble can be a little cold. So throw some heritage rugs around, put up paintings and tapestries, and put a lot of plants around. You could also tailor your deco to what your shop sells - if you decide to sell plants then you can make a rooftop garden with elven benches and put a fountain up there, etc.
