I've sadly determined that all of the pepper leaf wilt I've been getting that wipes out 90% of my crops is likely from an infection that all the silver maples around my property have on their leaves that drop all summer (luckily it only seems to affect the peppers).
My favorite crop are my hot peppers, I freeze most and use all year...so the solution I've determined is 5 gal. bucket gardening. One bonus of this is I hope to winter the grown peppers indoors in a pruned and dormant state and so get a longer season the next year as well.
I think this solution will keep the virus out of the soil where the main infection comes from.
Does it make sense to mix some biochar in with the pot soil? Will it still have all the benefits of in-ground biochar?
Biochar makes sense here. Biochar absorbs 5 times it's volume in water. Container plants get too dry very quickly. Also, biochar will help the drainage, which I'm pretty sure peppers need.
I would also consider using compost tea. If you add a few of those leaves to the brew, it will help inoculate your plants against that disease. It sounds like it's a fungal disease, so I would aim for a fungal compost tea.