With the MIB 1.3.6.1.2.1.2.1 -

.iso(1).org(3).dod(6).internet(1).mgmt(2).mib-2(1).system(1).interfaces(2).ifNumber(1) - you can get the number of interfaces.

For each PPP session there will be an additional Virtual Access subinterface, so you can obtain the number of PPP sessions by subtracting the number of "normal" interfaces (number of interfaces when there is no PPP session active) from the value got with the MIB.

With the MIB branch 1.3.6.1.2.1.2.2 -

.iso(1).org(3).dod(6).internet(1).mgmt(2).mib-2(1).system(1).interfaces(2).ifTable(1) - you can get info from all PPP-related interfaces (to get the the traffic volume on an E1, simply add the traffic volume on all Virtual Access subinterfaces establish over that E1).

Hope that's enough...