Personally, I'm running MongoDB & Mongoose for my server's data. I've used it for web projects in the past, and it tends to be the first thing I reach for to manage persistent data. I don't think it's a bad choice for your server's data.
MongoDB could be considered overkill for a project at the scale of a RageMP gamemode, since some of its features are mainly targeted for scaling a large app, but I dont think there's any harm in using it. If you haven't used it before and aren't familiar with it, but do have experience with SQL databases, then something like PostgreSQL with Sequelize might be a better choice in terms of getting things done faster. If you want to learn MongoDB just to build that knowledge for use in other areas outside of RageMP, then I think a RageMP server is as good a place as any to learn about it.