base RAM usage down super low (50MB to 100MB range)
A base Debian system (minimal netinstall with nothing selected in the tasksel step) doesn’t use much more than this, or at least it didn’t in the last stable release. For https://dnstools.ws/ I have a few VPSes with 256MB RAM that run Debian and the DNSTools worker. They run fine.
Dual-booting works fine. You can even have more than two OSes - for a while I was running Windows 10, Fedora, and Debian. Ended up sticking with Fedora.