You should be contacting an engineer. I know this is a DIY site, however, this part is not DIY.
You live in tornado alley, something which needs to be considered as this will effect the building.
Your on the right track with through bolts and ledgers, just get someone who is there looking at the project and spend your $$ wisely.
Also find out what your Building official wants to see in your location.
Certain sized bolts, threaded rod and washer sizes will be answered by the engineer. Probably around $400-500. $$ well spent.