Stick with the Thermador 14" or the less expensive (less features)14" Bosch. How long is your ductwork? You want the shortest run with a minimal amount turns. I have the 36" 14" Bosch with my 36" Miele induction cooktop with a 600cfm inline blower and have been pretty happy with it. I would recommend that anything you are doing which emits a lot of grease, you use the rear burners. My downdraft is catching nearly all (95%+ of what I can see) of the grease and vapor when I use the rear burners. The front burners are about 50/50. I still think this is preferable to a recirculating overhead hood.

We had a Thermador range with an integrated downdraft for about 14 years, in the peninsula. I liked the arrangement so well that we kept the location of the stove, refrigerator and sink for the remodel. We also kept the Thermador to use in the new kitchen. That was not a good idea. The stove had problems almost immediately when it was reinstalled. The downdraft was doing fine. Now we had a real problem. We had to replace the stove, but finding one that would fit was a problem. That wasn't the biggest problem for us. We thought we were going to have to install a hood. Our kitchen is at the end of a long room and I remember how I hated the overhead suspended cabinets that were in the original kitchen. I just didn't want something hanging from the ceiling and destroying the view. Since we are old, we wanted a range with a self cleaning oven. It was hard to find one with our specifications that would fit into the space designed for the new kitchen. We bought a Dacor range with a Dacor downdraft. These are separate units. I love the range and the downdraft works perfectly, for us. Long story to get to the point. When the new stove and downdraft were installed, the installers left the vent pipe with the opening upside down on a piece of wood under the house. That mean the downdraft did not work correctly. We could not figure out the problem, so my husband crawled into the crawl space and took pictures. I guess they figured old people would never figure this out. We had to hire another company to redo the venting. They took the vent pipe straight out to the side with no turns. It works perfectly. It even vents the steam from my rice cooker that is on the counter next to the stove. My point is that if installed correctly, a downdraft works.

We had a 25 year old Jenn-Air downdraft just like yours and also worried about the poor reviews and reliability reports we had seen on the current models. However, we had no options for any kind of updraft as the range is in an island in the center of the kitchen with lights (but no fan) above it. So we bit the bullet two years ago on a new downdraft Jenn-Air (the only company still making downdrafts) and it's been fine so far. Two pieces of advice: Don't get a recirculating anything - they are worthless! Downdraft is next to worthless but better than recirculating! If you can find a shallow shallower range hood, go for that and vent it out of the house if at all possible. You should be also able to get a custom made wooden hood to match the cabinets with the innards of a standard hood. The Jenn-Air will cost around $3500-$4500, so better keep looking for a good hood solution!

Your design is very much driven by wishful thinking. I understand. I've been there before. You'd really want it to work this way, and it's frustrating that nobody makes the appliances you want. A downdraft hood is close to useless, with one noteworthy exception, all recirculating hoods are no more than expensive white-noise machines, and even if you could fit in that place, a wall oven really doesn't work well under a countertop let alone under a cooktop. Pretty much the only thing you have going for you is the induction cooktop. That's a solid choice. I suggest you go back to the drawing board and pick a more conventional set up. A induction cooktop, a vent-a-hood recirculating island hood, and a wall oven at countertop level should result in a much more functional kitchen.