If you choose the two separate units you will HAVE to rewire. Your feed cannot supply the 240 for the wall oven and the 120 for the MW. I'd personally choose the single oven and the Advantium. The Advantium will become your go to for almost everything except large meals. And yes, it's worth it to rewire.

In my previous kitchen I had a gas stove with a single oven. In my new kitchen I have a GE Profile wall oven and the Advantium 120. This set up works great for me. I often roast vegetables using the speed cook option while I have something cooking at a lower temperature in the regular oven.They turn out great. I have also used the Advantium speed cook for things such as fresh pizza, pork chops, fish, potato dishes, quiche, lasagna and other entrees. I have used its convection bake setting for things like brownies and cookies. There is some learning curve for using the Advantium. Just recently I decided to figure out the custom recipes option and it is nice because once you program it you do not have to enter cooking temps and times for your own recipes the next time you make it. You do have to change out the microwave glass tray for a metal tray when using the other cooking options. And remember that the microwave wont be available when using speed cook or convection bake/broil. so you have to plan for that if you also microwave a lot. I know that GE appliances aren't generally favored on this forum but I have been enjoying both the oven and Advantium. I absolutely love using the built in probe feature of the wall oven. Meats come out perfectly done to the temperature I set. Here is a picture of my oven set up. The door under the oven stack holds the Advantium accessories.

Most importantly, dry them well before you put them in! Pat them with towels rather than just draining, and leave them sitting out for awhile if you can. Many of the vegetables that are good to roast have a lot of water in them, so do steam some anyway. Even though caramelization happens at 350° F., boosting the heat to 360° might help. I have a number of recipes that call for that, and I've been pleased with the results. Also, a little (importantly, not a lot but just a little) light oil helps the sugars to brown. Suntan lotion. :) I use "light olive oil", and safflower is great. Corn and peanut oils are heavy. Canola is in the middle. It's the viscosity that seems to matter for this.

@philbekins, yes, people do love their Miele around here! I've mostly been looking at the GE Advantium and Bosch as an option since people rave about those and the price is better than Miele. The Advantium seems to get talked about most, but I can't figure out if it meets all of my requirements. I think it would also pair well with this oven: https://www.ajmadison.com/cgi-bin/ajmadison/JT3000.html (though I still have to figure out if the speed oven + wall oven would be able to mount flush into a 30" cabinet).