Limit concurrent IPSEC VPN / IPSEC SSL

Hy!
I am looking for a solution working with up to 2.500 concurrent IPSEC VPN Tunnels.
Is this even possible with an Astaro Box?

I think the best choice is to use the software version (unlimited licence) and 1(2) nice small 1he server boxes with good nics (which one?). Or does ist work with one of the UTM Appliances? I saw different numbers regarding the max. concurrent users e.g. on the UTM 525.

Besides, there will be low traffic for each IPSEC VPN connection.
Any comment is appreciated!

Besides: I am also looking for a ISDN Dial-Up solution (up to 300 concurrent connections)...

Thanks