Hello!
Normally the changes are applied in a matter of minutes and they do not require re-connections, the forward rules are "hot swapped". However, your description hints at an undue delay, we will investigate. In order to speed up the change, if a similar problem re-surfaces, please disconnect and re-connect your system to the VPN server(s).
Provided that your forwarded port(s) are enabled for all the "devices" of your account, that the forward rules are applied for all the various VPN interfaces, and that you know which exit-IP address your service is reachable on, the multi VPN configuration is not a problem. If you find that port forwarding works with a "single VPN" configuration, but stops working with a multi-VPN setup, you need to check the above again.
No, this is not a cause for concern. Just keep in mind that without VPN DNS you can't use the AirVPN DNS based blocking system and the geo-routing system.
Kind regards