I offer these ideas without having done a dio myself, but I have many models in work and plenty of ideas for dios. So here's my take:
Will I have too many vehicles?
I think so. IMO a dio should have no more than 2 vehicles. With the number of models you have and their accesories you will be constructing for quite some time.
Would a workshop far back from the front have this much stuff?
Dunno. If you can find a photo or old video, that will help. However this takes away from your imagination. The whole idea behind a dio is to recreate an "event" so a photo helps here.
Am I suffering from advanced modeller`s syndrome?
Yes. Seek help immediately!
Will my wife kill me for spending so much dough?
Tough question. If your wife is making statements such as, "Why do you spend so much money on toys?", "Why don't you buy ME something?", "You spend more time in your (model) workshop than with me!" "I want flowers!", then it may be too late. You are doomed. You must find that delicate balance between keeping the woman pleased and keeping your addiction (modeling) funded. Good luck.