I think that if you use pistons for just a push and pull like a trap, it would not cause lag or if it did it would only be for the time taken for the circuit to do its work. Put if you are using pistons for a clock, the clock moves faster and faster which makes everyone re adjust to those constant changes of the clock. But anyways, I think the payments for the faction are not a good idea except for the land purchasing and faction making. Less shit factions would be on the server with the purchase and with the land claiming, people are less apt to buy all the land in sight.
Like Rokku said above.