A couple questions...
1. What is the recommended best practice for the location to install Magento - in the root, a subdirectory, or a subdirectory with a bunch of htaccess directives to make the subdirectory invisible to visitors? Note that I currently have zencart in the root, with Wordpress installed in a subdirectory, and Wordpress posts are integrated into zencart. I'm not too worried about moving Wordpress to wherever I need to, but I thought I'd mention it.
2. I have zencart installed now in my root. I want to migrate to Magento. What do you suggest I use for a temporary Magento location before I make the live switch? I can think of a few options:
I'm thinking the first option, creating a new account, is the best for ease of switching/testing. Thoughts?
You can install Magento in any way you described: to a domain, to a subdirectory, or to a subdomain.
A technical information about installing Magento 2 into a subdirectory: https://mage2.pro/tags/subdirectory
I'll recommend either a new hosting account or a subdomain (where the files are located outside of the main domain).
I wouldn't recommend a subdirectory because any .htaccess files in the main directory may affect the subdirectory as well, making troubleshooting a little more difficult.