Agree on Dell. I'm looking at buying two computers and Dell is the only one I am considering.

To the OP: Those are light loads on any modern computer. About any consumer-grade model with 8 GB RAM, ~256 GB of SSD storage, and a nice monitor will do. You can add a HDD, if you have a lot of data to store; even 1 TB is cheap. I am told that dual monitors are a must if you spend much time in the office. (That is the plan, here.) If you buy direct from Dell (or other reputable manufacturer) you will avoid much of the bloat stuffed into computers at big box stores.

For SMS and QB and other Windows-specific software, well, you are stuck with Windows 10. The Home version will probably suit your needs. As for antivirus protection, I am currently using Norton, Kaspersky, and Microsoft's own Windows Defender on various machines. My unscientific impression is that Kaspersky is the most ambitious (and intrusive), Norton uses the most resources (though that isn't as big an issue these days), and you hardly know Defender is there, doing its job. For no more than it costs, Malwarebytes plays nice with all the others and adds a second layer of protection.