The first step you should take is to solve the original problem. You need to make sure to get rid of the termites or confirm they are no longer active (if they were treated before your purchase).

Second would be to hire an experienced timber frame repair person to survey the extent of damage and recommend repairs. If the house is relatively intact, it would be worth paying the extra cost of doing the repair without removing historic fabric. This work requires a specialist.

There are several Guild members listed in the TTRAG membership list that might help you find the right person. Once you have found a potential conservation specialist, don't hesitate to ask for references and permission to contact previous clients.

Good luck with a great goal!