Pull-back of the meat from the end of the bone is the best indicator of done-ness with ribs. The amount of pull-back or meat shrinkage you want to see will vary with the amount of tenderness you want. Fall-off-the-bone ribs will have the most pull-back.
Also, slab bend test or sag of the slab when lifted and supported in the center of the slab will indicate the degree of done-ness as a quick check before removing from the cooker. Less sag indicates more meat shrinkage...the more shrinkage there is the more done they are.
I have heard of a few attempting to use a thermometer probe and compare the results of the temp with the amount of pull-back or slab bend, but never heard of the results. Temps are not easy to get from a thin slab of meat such as BBs or spares, especially with a lot of bones present, so this would be a difficult undertaking. It could be a viable option with heavier/thicker slabs of beef ribs, though I've never tried it with them, either.
I guess the next question would be how tender do you want your ribs and how to get them to that texture? Amount of tenderness is a personal preference. Then, do you want a bark (crust) on the surface, or tender all the way through. Different methods will achieve different results, and foiling during mid-smoke is one way to get a more tender rib with less bark, as an example. If you've read much on ribs here, you've probably seen the mention of 2-2-1 for BBs and 3-2-1 for spares. This is a commonly used method by many members here for getting a tender rib and setting the bark at the end of cooking...may not be to your liking having a bark and if so, omit the open grate cooking at the end, and extend the foiled time or initial smoking time, instead.
In any case, you should cook low & slow, not over 250* smoke chamber temp, and generally 225*, to achieve a tender rib. You can build on what amount of time and temp to use with some experimenting to get a rib you like best. Again, personal preference will determine which direction to go after trying a few different methods.
Well, that's a start for answering your questions...hope it helps.
Eric
EDIT: I see my distractions got in the way for a while and you have other replies now...man, things are chaotic here today.