trout,
Let's see if we can't address your specific questions before generalizing a bit.
1. "Material difference" between 300 and 500 btu burners: Very little, if any. The salesman suggested that the slower burner could hold couverture chocolate without scorching. Maybe. I doubt he's done it. I'd use a bain-marie, and so shoud you, and so should he. Besides, how often do you hold melted chocolate?
2. Diffusers? Yes, there are. Also a variety of tricks, like double boilers, to temper heat.
3. Do you need four 16,000 btu burners? Not at the same time, no. The greatest number of pans on high heat a
skilled cook can handle is equal to the number of eyes or hands. In my case that's two. For almost everyone without a lot of high-pressure experience, it's usually the number of pans that can receive complete attention. In your case, that's probably one now, and two in a year or so.
Okay, let's talk about
pro-style ranges in the home. The operative word is style. They are not professional ranges. They are insulated, they use a different type of pilot (a lot of restaurants leave the pilots off, btw), and they use a much smaller gas intake handling about 1/4 of the flow.
The intake diameter relates to the total output of the burners. You see, when a BTU rating is given by a stove manufacturer, it actually refers to the amount of fuel used and not the actual heat output of the stove -- not that those aren't
usually closely related.
However, unless you're using a giant wok, or use 14" pans to sautee, as a home cook -- even a very good one -- you don't need that much flame or heat. In the first place, you shouldn't have more flame than the diameter of your pan. Once it's coming up the side, it's not doing you much good. Instead it's blackening the pan.
For a restaurant cook, different story. In a restaurant you want to come to heat as soon as possible, **** the consequences, and you're not the one washing the pans. At home, you have the luxury of allowing a pan to come up to speed a little slower. The kicker is whether the stove has enough power to bring your pan back up to a fast sear after a cold piece of meat comes in. And 16,000 BTU should be more than enough.
Pro style residential ranges are more complicated than actual commercial ranges and "regular" home ranges. Consequently they tend to need more repairs. But because of their cost there (a) aren't that many around, and (b) the repair people figure the owners are fair game. As you've found on your own, Thermadors are notoriously fragile and expensive to repair. Other stoves may fare better. Also, the situation may have changed over the years, but it used to be common wisdom that Viking repairmen's children had straight teeth and went to college without taking out loans. I think that's fairly typical.
On the other hand, pro style ranges often have some fairly neat gimmicks -- like real griddles and grills on the stove top -- that you can't get in a regular range. They also have killer styling and beaucoup prestige.
But when it comes to actual performance, don't kid yourself. A Wolf residential isn't much different from a Frigidaire or Maytag beyond marketing. In fact, few commercial manufacturers don't actually make the residential stoves using their names. Wolf residential, for instance, is made by Sub Zero. while Wolf commercial is made by Wolf. Typically the only components that cross the lines are knobs and badges.
As a consumer, buying a complicated, high-ticket item like a stove, it's easy to start inventing distinctions where there isn't really much of a difference. That's what marketing, hype, and sales people working on commission are all about. Now, I'm not saying don't get one. The styling, the gimmicks, the heavy duty grates, etc., they're all worth something. Just try and keep some perspective. Don't spend more than you can comfortably afford on a stove, it won't make you a better cook.
Bottom-line useful are:
- 1 slow burner;
- 2 fast burners;
- Easy to clean top (that is incredibly important), preferably with "sealed" burners;
- Same-height grates allowing you to slide pans from one burner to another;
- Self cleaning oven;
- Convection; and a
- Good broiler
After that, it's mostly a question of having the right assortment of pans and
baterie de cuisine. Save some dough on the stove. Also, save some dough on the pans. You don't need copper, and you don't need the finest All Clad either. You don't even need a "set." Be canny.
What to do with all that money I just saved you? Get a couple of John Boos cutting boards, an excellent chef's knife, and a way to keep all your knives sharp. Get your wife a present. Don't deny yourself kitchen gimmicks. And towels, get plenty of microfiber towels. Those suckers kick @$$.
Good luck,
BDL
Understanding Ranges 
