(I’ve moved this to projects so you can get individualized answers based on your particular setup.)
I’m tired today, so I’m not going to give you a very detailed answer right now. I’m sure others will chime in. 
As far as high-end switches, you might also look at the Cooper aspire line. Eaton is the Company, Cooper is the division, and Aspire is the model line. The switches might be listed under any of these names.
Decora
Regarding Leviton, “Decora” is their trademark name for any rocker switch. It could be Z wave or not. I think the question you were asking is between their high-end “vizia” line and their lower cost zwave line where the devices start with the letter “D.” The difference is that the Vizia line has instant status and the lower-cost line does not. The Vizia models start with the letter “V.”
Shopping
As far as where to shop, Amazon is not always the least expensive. Check with the specialty home automation retailers, a number of them offer volume discounts.
Home Depot and Lowe’s also carry some brands, and it’s worth checking with their contractors desk to see if they can offer you a volume discount also. This may depend on the individual store, I have had more luck with this going into a store and asking as they may be able to place it as a special order with the discount.
Multibutton switches
First, you don’t necessarily want “scene capable.” That’s a zwave specific term but because SmartThings is a multiprotocol platform, any multibutton device that reports its button presses to the hub can be used to control the equivalent of scenes. And some Z wave “scene capable” devices don’t work well with SmartThings because they don’t report the button presses to the hub. It’s best to just leave that term out of things.
See the following FAQ for various multibutton devices That do work with SmartThings
You should be able to get the kind of control what you want with pretty much any of these, although there may be a slight lag, that’s another complicated discussion.