Openvpn – How to configure multiple address pools for OpenVPN server

Debian-based systems should be able handle multiple VPN connections just fine. Just put the configs in /etc/openvpn/*.conf. If you haven't modified your /etc/default/openfile then the startup scripts will startup an instance of openvpn for each *.conf in this directory.

Of course this assumes that your various VPNs don't have conflicting routes or configuration that prevent each other from starting properly.

Is it possible to configure the server so that when clients log into the VPN they can use the same network names as the server?

No, hosts files are typically for local resolution only. If you need to provide name resolution services to clients, you'll need to set up a proper DNS server.

Dnsmasq is a relatively simple, low-footprint option that is simple to configure. It can be configured to read its configuration from the server's /etc/hosts file.

It is a good solution here to set such addresses in the client's /etc/hosts.

No, it is never a good idea to do this outside of very short-term things.