How much pepper sauce could you get out of a Carolina Reaper?

Pepper sauces usually deliver an aroma (from the peppers), some sweet/sour/salty element (from the pickling ingredients mostly), and heat (from the peppers). A hotter pepper will not necessarily be stronger in aroma, so using this kind of super hot pepper alone can end you up with a sauce that is hot but poor in flavor. Also, given that capsaicin is very soluble in fat but not very soluble in water/vinegar, such a sauce will have a very uneven distribution of heat and will likely end up with a very harsh, unpleasant heat no matter how diluted - similar to throwing chile powder into a lean soup.

How much sauce could you actually make from one such pepper?

Too many variables at play to answer definitively. The most influential variable is how many Scoville Heat Units (SHU) you want your resultant sauce to be.

I would personally remove the seeds to improve my seed bank.

Most of the Capsaicin is in the seeds and the pith they are held by (https://en.wikipedia.org/wiki/Capsaicin#Natural_function). If you remove that for a seed bank you are removing most of your heat.

Is there a general rule of thumb for how pepper sauces are made in regards to the SHU levels they achieve?

No general rules that I'm aware of. Again, depends on how hot you want it. A quick google showed me hot sauce recipes averaging 6 Jalapeno's to make 8 ounces of hot sauce (adding vinegar and other things as well).

My guess: if you wanted to make a hot sauce of Carolina Reaper level heat, you would use 6 reapers for each 8 fluid ounces of product..... I know I would have little interest in using that sauce.