To expand on what @hansen provided (thanks for the mention -- much appreciated!)
a). How Many Sites Can I Host?
As @hansen noted, it really depends. If the sites are static sites, hosting 20-50 sites isn't going to be an issue. If, however, they are database-driven sites -- WordPress, Drupal, or another CMS -- 1GB isn't much to work with. It really comes down to how well you tune your stack.
I've ran a few web hosting companies and side businesses in the past 15 years. There have been times where hosting 100-400 sites on a well-tuned server are not an issue -- in other cases, on the same hardware, only 10-20 sites could be hosted. There's a lot of variables at play and you have to keep a close watch on pretty much everything.
One of those companies was geared specifically towards WordPress sites. It was before the larger and more funded companies really came on to the scene (WPEngine, Pagely, etc) -- before there was really a "WordPress Hosting Market."
When it comes to WordPress, the CMS itself really doesn't use much. When you start adding a ton of plugins, backend services, etc -- that's when resource usage starts to rise.
Most of the single-server instances I ran had a single Quad-Core Intel Xeon (w/HT), 16-32GB RAM, and 4-8 solid state drives in RAID-10 -- with a separate server for backups in another data center. That was generally enough to host quite a few basic sites, until traffic increased and they had to be moved to their own instances (though some sites, on that server, were handling 1-3m visits / month, before moving them, without a single issue).
I was doing this with cPanel since I needed more automation at the time and I didn't have the resources to build out my own setup (i.e. funding).
Now days, I'm aim to build out my own over using cPanel and I'd use NGINX, PHP-FPM, MariaDB and a cluster setup with load balancing -- something cPanel can't do (same for most control panels).
With 1GB of RAM, I'd say you're looking at 3-5 WordPress sites comfortably, if they are low-traffic instances. Beyond that estimate, it really depends on how the sites are setup, how the stack is tuned, and what your plans are for the build out.
b). DigitalOcean is 100% Un-Managed
Like AWS and competing services, DigitalOcean is also un-managed, meaning that when it comes to your server (Droplet), you're responsible for setup, security, management, etc.
Services like CloudWays exist to simplify some of that for you, though they do not provide root access, so you're a bit limited on what you can do and a sysadmin isn't going to be able to help you with them because of that. I've tried to work on some of the configurations they deploy for previous clients and it's not possible. They lock you out of root and do not provide a standard sudo user for you to use to install or modify services, software, etc.
I ran in to an issue with one client that needed MariaDB tuned for their stack as their default wasn't cutting it -- it's not going to happen. They told me the client can upgrade to get more RAM, but that's pretty much it. Throwing hardware at an issue will only work for so long -- it then becomes more costly to throw hardware at it than it would be to hire someone to actually get in there and tune it.
With DigitalOcean along (without going through another service provider), this isn't an issue. I, or any other sysadmin, could login and work with you.
That said, if you want some information, feel free to get in touch, I'm always happy to work with clients as much as possible. The only day this week I won't be available is Thursday as I have a final interview scheduled for DO ;).