First of all, Data Protector A.08.10 and patch bundle 8.12 on top seems to be pretty stable. Works quite well for many of my customers now for upgrades and new installations. Stay away from A.08.00, since it has some glitches that might hit you hard.
If a session is started, a xSM process is started on the Cell Manager that takes care of the inserts into the IDB. Having 4 concurrent sessions is nothing that would stress even and old CM to much. xDA and xMA proccesses will consume more memory and CPU resources, while Data Protector in general seems to be very economically.
Regards,
Sebastian