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.