I am dwelling on how to scan future tenants and what to have in my lease agreement and more.

Validate zoning, potential special or use variance, future zoning map, neighboring zoning.

If they close and sign up with us then we do a site walk etc and begin onboarding.I am also a broker who assists in finding the property, doing walkthroughs etc and I get paid a commission at closing from seller.Long story short I would expect them to give you an analysis of properties you are interested in for free based on the hopes of future business, if you want them to go above and beyond and attend showings etc then ask them if they are interested and offer them compensation for their time :)

I would consider partnerships in the future.

Save for future expenses, especially if self-employed6.

Most likely you will regret selling your duplex in the future, so seldom sell and try to find a way to keep it.

Any advice on how to get rental income reported (from the current rental property and future income from renting out our primary residence) and lower the DTI??

As for getting a HELOC, it's prime + index (fluctuates based on the market), so to answer your question, if you are able to qualify by yourself, then it's always a better option to get a loan solo, then use your spouse's income as a backup for future investments. 

I hope to talk to or run into any of you in the future.

They remain available to assist investors throughout the investment lifecycle, whether it involves refinancing options, addressing financial concerns, or facilitating future funding needs.