Umm, I don't think you will find a "simple" solution, but here are some starting points....
What you are looking for is quite possible, thats the good news.
The less good news is that the parts/modules will get expensive unless you design, build and program your own devices.
So look at http://www.electricIMP.com
their neat little modules allow for basic sensor input into an http service. You will need an account and a breakout board and some other bits and pieces to suit your sensors.www.hobby-boards
make some nice, but expensive 1-wire sensor boards
Search Digikey or Mouser, etc for 1-wire components such as the DS18S20 for 1-wire digital temperature measurement. I don't think it will handle 300F though.
Search Digikey, Mouser, etc for LM34, LM35 analog sensors- these are inexpensive and accurate when properly implemented.http://www.Adafruit.com
sells fluid control valves.
Going deeper..... Arduino UNO is a good base platform to experiment with. Be careful about sensor voltage, vs. your MCU voltage though. Shields are available to connect an Arduino to the ethernet and through a POST command, data can be sent to a web server somewhere to process and display, store in a database, send error messages, hook up to twitter, messaging or even your local 911 if you need to.
I would suggest you use 1-wire for your sensors and control since the wiring is very simple (i.e. a daisy chain), vs. I2C or serial.
An alternative is the Raspberry Pi, if you can get hold of one. It is a UNIX based MCU on an I/O board with ethernet embedded.
Good luck and please let us know how you get on. Don't breath in the magic smoke!