I have tailscale, which is great for ssh-ing onto my Nas from the outside world. But to access my services, is a VPN the best way to do it?

The main point about Tailscale that I see people on here often get wrong is that they compare it to a “classic” hub-and-spoke VPN, when in fact it is an end-to-end zero trust encrypted mesh network. End-to-end does not mean machine-to-machine, it means user to service. So in your case, you should place one tailscale node in each pod (collection of containers that make up one service) as a sidekick. That way, a user need to authenticate in order to even open a network connection for a specific service, which is a very secure solution.