The best system available is the Enviromon System. This is a standalone unit. The EL005 data logger can measure upto 250k samples. It has a maximum sample rate of one per minute and can have upto 10 convertors connected.
To measure the temperature in the rooms, depending if you need to take more than one temperature in differnt parts of the room then I would advise an EL001, which will allow three temperature sensors to be attached. If you only need a central temperature reading I would advise on a EL026, which can measure one temperature and a humidity.
To measure the current there are a few options you could use the EL040 current monitor, unfortunately it is only able to measure upto 300A.
You state 400A in your description, it would be possible to use the EL037 and the 600A current clamp. However, to do this you will need a 4mm connector to connect to the current clamp and the other end of the 4mm connector will go to the EL037 screw terminals. This unit only measures positive voltage so you would only see the DC side of the current. An alternative current clamp could be sourced from www.RSWWW.com
which will turn AC current into a DC voltage.
The system connects together with network cable, but it is a closed network only applicable for the Enviromon system. The maximim distance between the logger and the convertors with the network cable provided by us is 400m. This can be extended up to 1 km if high grade network cable is used.
The units I would recommed will really depend on how many temperature sensors you need in each room, the distance appart that they would have to be. They Current Monitoring option you would like to use.
For the fist tank I would recommend the EL026 and the logger I would also recommend the EL005. This system has been designed so that it is extendable. So more convertors can be added and alarms if required.
Please email me further details, so that I can advise further.