The website is single page. No complex backend. At most it fetches stuff from another web service and does some crawling/crunching. I don't expect high loads here.
Mainly asking for the website self-hosting purpose only.
Can I downgrade here? Also just wondering what do most people use a 1cpu 0.5gb machine for? VPN? Personal website? Or something else?
You can push quite a lot on such machine. I used it as a shell access for my stuff from any place in the world, instant messages, IRC. Classic IM networks died so that part is gone as well, but a VPN like wireguard is a great choice.
A small monitoring system should fit.
A clean install of mariadb or postgress is around 40-60MB of RAM as far as I recall. This should open some doors as well.
A webdav/carddav/caldav server should also fit. I am about to check sabre/dav (sabre.io) software on a similar machine. So you can have a selfhosted calendar or access to your files on the go. Webdav can be handled by a web server directly (natively by nginx or apache etc).
I am recently charmed by Archivebox app, it makes backup of a website using multiple methods. UI is a custom Django Admin interface. It takes below 200 MB on my system.
A Teeworlds game server, if you are nostalgic towards quake but want a simpler experience for a break with friends.
Make sure to checkout the list at GitHub under awesome-selfhosted/awesome-selfhosted. Many, many inspirations there.
For static website I suggest cloudflare pages! It's free, fast, and easier!
It should be fine if your backend is not doing any memory operations
If you want to host another website, you can do it but just keep it static no backend involve
Web Server for mostly static content (.html files, etc.) (e.g. using nginx).