Your existing Apache setup can be used as a reverse proxy. The idea is, you setup those other services (eg, next cloud or radicale) on other systems, or on the same system with different ports. Then when you access some URL, eg https://yourhomenetwork.com/radicale, Apache acts as an intermediary and returns the service at http://127.0.0.1:8080/radicale. No additional open ports needed. No additional certificates needed.
Apache can even be configured to respond to requests differently if they’re coming from the internet or from wireguard. Say if you wanted to deny all traffic from the internet and only access it from your VPN, or if you wanted to conditionally apply a password.
You can also use Apache to host multiple domain names, or sub domains, from the same IP address and ports (the feature is called “vhost”). That may require multiple SSL certificates though. (EDIT: If youre using a wildcard certificate, you can host multiple sub domains from that one certificate)
You’ve got options though, and you don’t need to break what you’ve already got :)
Absolutely! Yes you can :) Good point, and I will now change my comment for greater accuracy.