Advice On Negotiating Repairs With Seller

[Diana Tran]

THIS WILL BE MY FIRST HOME PURCHASE. THE SELLER HAS A REPAIR COUNTEROFFER.
I'm not sure how to proceed, any advice would be greatly appreciated.

About the house: It's in Tampa, a duplex. Unit A is about 100 years old and Unit B is almost completely new.

Pros:
-The duplex is in a very desirable neighborhood with home value appreciation year over year at about 50+%
-Rent is also in high demand within this area
-Cash flows well even with high interest rates and increasing property taxes
-Home is price below average cost per sq ft
-The house has been renovated and some parts of it has been remodeled

Cons:
-All issues are with Unit A, the 100 year old unit.
-Has no crawlspace (common for older properties) so we couldn't see the foundation
-Drywood termite/wood decaying fungi damage seen on all the windows/doors/parts of the beam on the exterior, parts of roof decking and rafters in the attic
-Old leaks/moisture damage seen in the ceilings and attic
-Parts of the roof has patch work
-Roof doesn't have any permits on record (don't know how old it is)

Seller's offer to me:
-Fumigation treatment for drywood termites (tenting the house)
-Replace and repair all damage wood throughout the house
-Replace the entire roof with a new permit
-Replace one window in every room (not all)
-Pay for a structural engineer to inspect the foundation
-Offer to get quotes for repairs and have a 15-20K budget to make all repairs, house is 500K.
-Will be open for us to extend our inspection period

The counteroffer sounds attractive since he's offering to pay for most of the repairs, even for an engineer to properly inspect the foundation. However, there's still hesitation from my side. What do you think? How would you proceed?