A: MegaSpore should be enough. It's interesting because different probiotics, like the spore-based probiotics, don't need as many spores to do their job versus the lactobacillus probiotics. So, that dose sounds great, and I hope it's helpful for you.
I also have a few additional probiotics, including spore-based ones that I just created with Rootcology. I encourage you to check them out:
Rootcology ProB 50
If you didn't do well with S. boulardii, then you may want to avoid it. I would also look into doing something like an Organics Acid Test to see if you have a yeast overgrowth, and perhaps that's why you might be sensitive to it.