Hello...I think you want to put too many eggs in the one basket.
My preferred method is to use a dedicated firewall, not SME.
I recommend Smoothwall or IPCop, both of which are excellent firewall systems (small, free, work on minimal systems) which provide DMZ facility easily.
I use a P400 with 128Mb RAM and 8Gb HDD which handles 10 users really well.
Both have VPN ability, but IPCop especially can have OpenVPN (
www.openvpn.net) to give you external access....and there are contribs here on how to do it with SME which are probably transposable to IPCop. I guess Smoothwall can use OpenVPN too, but is more tightly controlled about updates (which might knock out the OpenVPN).
Cheers
