No you can't set different sample rates and the memory question is a hard question to answer as the device uses compression so record length can vary. Why do you want high sample rate for temperature. Temperatures normally do not change very quickly so do not need a high sample rate. Things like amps though which spike quickly need a high sample rate or you can miss a complete spike. I would say just put it on the highest sample rate and don't worry as recording some items at different sample rates won't make a huge difference.