If you are going to use mydomain.info both internally and externally then this is possible and is known as a 'split horizon' DNS setup. This requires the use of two DNS servers, one for use internally, and one for use externally.
As an example, a client device would be connected to the Internet and ask a DNS server what is the IP address for vpn.mydomain.info it would then use the answer to connect to your VPN server. What you then need to do is have your VPN server tell the VPN client to use your internal DNS server while connected, this is possible with most VPN servers including Apple's rather weak one. Then your VPN connected remote client will be able to ask your private internal DNS server what IP address to use to talk to internal devices like your Open Directory server and perhaps a file server.
Screen Sharing normally uses Bonjour which does not work across WAN or VPN links, or at least not without a lot of pain. If your LAN computers all use static IP addresses - perhaps assigned by a DHCP server then you could setup fqdn records for them which could then be used for Screen Sharing, e.g. comp1.mydomain.info. The way I handle this is to Screen Share to a server which of course has a static IP address and hence can have a fqdn. I then run Apple Remote Desktop Admin on that server which can scan for all the Macs even if they use dynamic addresses and then allow me to control them.
If you are going to have a server like www.mydomain.info or mail.domain.info which will need to be accessible both inside and outside then you need to remember to add this to both your private internal DNS server and whatever external DNS server you use. (I use networksolutions.com as the seller and host for my external DNS function.)