The problem I have with 3rd party collecting is the potential claw-back of rent by a "professional renter" plus my lender needed more information and disclosure to match the funds collected versus directly coming to my account as I do now.

The problem is with my Closing Disclosure. 

I don't know anything about properties that old but you should be getting hopefully a property disclosure from the previous owner.

Currently, I requested my buying agent to send a Notice to Perform to the Seller for additional disclosures and other details regarding past remodels but the agent is reluctant to do so. 

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Texas clarified their laws to require full disclosures and some other states are now working on disclosures docs as well.

UT is a non-disclosure state so it's hard to get too close but I've been tracking sale comps like a hawk in a spreadsheet for the past ~6 months and think it's right around there.

How common is it for sellers to not provide disclosures?

Full disclosure, I've not hired him yet but he comes highly recommended by some colleagues.

What are things to watch out for in loan disclosures and what can be negotiated and compared with other lenders?