Every spring you see the masses flock to the garden centers buying grass seed and fertilizer. Fall is the time if year here in the mid-south to make changes to lawn care. Like Sparky said, summer heat will waste most of the spring progress.
Vents only work if you have an unrestricted area for air flow. Attics need to have intake (lower) and exhaust (upper) to create a chimney effect. An engine has an intake and exhaust manifold, compromise either and the motor won't run or runs inefficiently. Same for a roof structure. Do you have...
The wood decking will dry out. You have air circulation underneath. Did you have any interior damage to the house from water? I'd be more than a little upset.
Cut out the bad sections, replace with pvc and use Fernco fittings to mate the cast iron to the pvc. PVC comes in 10' sections.
https://www.fernco.com/plumbing/flexible-couplings
Fall is the time of year to plug the yard and overseed the yard. Grass sets its root system during the cooler months. You can try weed control, but, summer heat will stop grass growth.