Disclaimer, I sell all listed brands for a living, but the reason I recommend them is because I know them and trust them.
We've designed and built a lot of custom kitchens. I myself am working on one for my house that will have a YS640, a pizza oven, a power burner, a fridge, a sink, plus plenty of dry storage.
The built in ceramic grills (Primo, BGE, Kamado Joe) are very nice, and are very versatile, though (IMO) they lack space for the money. Have you thought about a charcoal built in head? There are a few out there that are quite nice and won't break the bank, then you can have a smoker that is a bit more portable for convenience.
Also, don't think that you have to spend $4k to get a nice built in gas head. Check out the Napoleon Gourmet Grills line. Their built-ins start at $899 and are incredible cookers for high heat grilling and such. Plus, if you want charcoal, you can just add their charcoal tray on one side and cook with either or.
In other words, there are a lot of options out there, so take some time and make sure it has everything you would want before you start building.