I did not see a relay power spec. It is nice if they can handle 8-16amps, otherwise you might need another relay to switch the higher currents. At first I didn't think it had a data log file, but it does. It outputs the data every 24hrs, I guess if your monitor is not there the log data is overwritten. It does mention "your software" does that mean low level machine control or object orientated code? Looks like a good place to start (are you OK with the system requirements? They look a little thin). I think you can control pretty well with two channels of temperature that would leave you two other for storage data. I did find that the Control by Web data logger only provides 8 channels when in logging mode, if it is placed in control mode it only has two temperature channels as control channels.