I am a 26 year old software engineer in Miami, Florida, looking to make his first deal in real estate happen.

I am curious, is anyone using any kind of software to infill mobile home parks?

The ability to work from home is undoubtably increasing, disregarding COVID, remote work will continue to grow as businesses look to lower costs and software continues to improve.  

Once you have a property you will most likely hire a property management company for a month % although I know people who have a smaller portfolio that have local leasing agents and handymen connections to do the important parts of owning property and they just purchase a PM software to save money.

A lot of contractors do not utilize an estimating software to make it easier to provide a line item estimate.

If you get audited, there will be questions and you need proof.

Does anyone know a software/website that offers a paid version of a nationwide screener?

This is just my opinion, maybe others have great luck with software.

Now, if you are looking for duplexes, triplexes, and fourplexes, then the whole MF mailer strategy should work and any one of the software you mentioned is fine.

All of the accounting software seems like pretty serious overkill for a single-member LLC that flips houses and is taxed on a Schedule C form.