Adding services to an existing Docker nginx container

Hi, I'm just getting started with Docker, so apologies in advance if this seems silly.

I used to self-host multiple services (RSS reader, invoicing software, personal wiki) directly on a VPS using nginx and mariadb. I messed it up recently and am starting again, but this time I took the docker route.

So I've set up the invoicing software (InvoiceNinja), and everything is working as I want.

Now that I want to add the other services (ttrss and dokuwiki), should I set up new containers? It feels wasteful.

Instead, if I add additional configs to the existing servers that the InvoiceNinja docker-compose generated (nginx and mysql), I'm worried that an update to Invoiceninja would have a chance of messing up the other setups as well.

It shouldn't, from my understanding of how docker containers work, but I'm not 100% sure. What would be the best way to proceed?