Rules on redstone

Sorry if this is in the wrong category, I don't know if it is really support. Anyway, are there any limits on types and amounts of redstone I can use? Are large hopper systems okay, like sorting systems? Are redstone clocks of any kind allowed, and if so, is there a preferred clock? (eg. Hopper clock or observer clock)
I just want to make sure I will not be a source of lag.