Investor hours alone (reviewing documents, reviewing financial statements etc) without that person reviewing then going and taking action does not count.   

Other than that, mistakes related to expenses are common, and not electing things like the De Minimis Safe Harbor election, which can save you if you get audited.An option you might want to consider if you do your own taxes is at least have a tax professional review your return after you complete it (but ideally before you file it). 

We as a firm have investors working with us who have rental properties all over the US big and small.Finding a real estate-focused tax professional and one who can help with advisory and grow with you would be my suggestion to focus your efforts on finding.

My fiancée and I will be beginning our real estate investment journey in 2024 and are looking for any suggestions or pointers as we make some of our initial decisions.

They may also challenge the sale (maybe they weren't properly notified.)I suggest you read the tax sale laws in your state. 

If you have a deal that you think is more valuable than you think it's worth and want to sell it on the market, I'd suggest closing on the place.

Any advice or suggestions? 

As a new agent, I suggest going with a big brand name brokerage that has good training like a Long & Foster (Who I work for), Keller Williams, etc.

My lawyer suggested responding no to all the requests and send her on her way - it wasn't worth the hassle.

Happy to review the deal for you if you want another set of eyes on it.