I have seen plenty of mosaic artists do mosaics on plywood (exterior grade or marine), frame them prettily with wood moldings like a painting, and hang them using something like keyhole fittings, steel cleats, or flush-mount brackets. You could also screw them in place using heavy-duty wall anchors (I like the EZ-Ancor metal screw-in anchors sold at Home Depot) where the frame pieces would go, and glue on the frame pieces afterward. This approach has been suggested in many places for portability such as if you're renting; it was discussed on Apartment Therapy and I've seen it in several magazines and on an episode of Home To Go. There are plenty of mosaic artists doing works on plywood backings and having no problems with cracking - go see the folks over on the Stained Glass and Mosaic forum here on THS. It can be done and don't let the naysayers get you down.

Just my two cents hubby and I have renovated 4 homes. The worst redoes were the homes with a backsplash. Those homes always looked the most outdated. I think counters and backslashes are usually the first things to run out of style in a kitchen. Much easier to tear out a counter then a wall with tile or laminate that someone put up with liquid nail. That being said, we are getting new granite counters and I did consider a tile backsplash. There are so many lovely choices now. We opted to just go with the 4 in. that matches the counters. Sometimes people paint the area between the counter and cabinets a contrasting color. That looks nice. I am grateful that the previous owners never put in a backsplash. It would have upped our costs on the counter replacement. The homes in my area were built in the 90's when pickled oak cabinets and mauve was the rage. My neighbor has a mauve backsplash. They just replaced the counters and decided to leave the mauve tile backsplash due to the work involved in removing it. Anyway, I think you are good without it.

Some electric ranges are approved for 0 inches to vertical surfaces above the cooktop, meaning there could be unprotected wall right up against the back of the range and cabinets on either side. They do have similar distance requirements to Horizontal flammable surfaces, though. (Overhead cabinets) So, according to manufacturer's specs, you may be able to use the vinyl backsplash with certain electric ranges. International Building Code minimums for vertical spacing defer to manufacturer specifications. Your local code may be more stringent.

Behind the sink and faucet, a big rectangular piece of glass framed with a stainless steel molding will look nice. It will be self-contained. Also good behind the cooktop under the kitchen exhaust hood. Any other material, arranged as a framed rectangle, will look good. This lets you have a washable wall protection which also defines a workplace spot and thereby adds interest. Without it, the space might feel a bit too undefined. And your wall may get grungy at those spots, over the long term. So you repaint. But the space feels undefined, loose and unfinished. Any long thin backsplash causes the space definition problem which you have identified: "As a result the middle wall ... doesn't really have an "ending" on the far right side...." A long thin backsplash surrounding the whole space causes other space definition problems. It's all a matter of tradeoffs and compromises.