If you want to start at a lower count probiotic, then it might not be so hard on the body. Maybe start at something between 15-30 billion per pill. Then go for something like 45 billion and up higher if you want. Its up to you, but it may cause more die-off.
Or just start at one pill per day and then go up to 3 pills per day after a few months…
The brand you suggested I have heard of; its actually made by renew life. They make pretty standard/average probiotics but it won’t have any drawbacks other than not having human derived bacteria.
As far as antifungals; I would add one at a time every few weeks depending on how bad you feel. Week 2: add garlic, week 4: add SF722, week 6: add oregano oil, etc…something like this.
I wouldn’t mess around with the brown rice flour. I would stick to the buckwheat/coconut bread and eventually you can try more foods as you get better. Veggies is one safe food item that you can have forever.