My lgc 3000 came with a T, terminator and extension cable (that I did not really need). LGC-3000 will get it's power when you connect it to the T which connects to the backbone. No other wires necessary.
The 200 or 400 setup comes with everything you need to install the gauge, nmea 2000 backbone and the extension cable to run the ep60 fuel sensor (plenty long for my 21' CC-believe I had to coil quite a bit of extra).
Yes, Lmf 200 w/fuel sensor + lgc 3000 will give mpg (as well as gps coordinate, ground speed, etc).
I have my 400 to display the fuel flo info on page 1 (gph + mpg + fuel remaining). Then scroll to page 2 for gps position (as a backup to my main gps).
Page 3 is my Speed over ground (nice and easy to reference while drifting to get my speed of drift) Nice and big in middle of screen-very easy to read
Page 4 is my trip fuel, seasonal fuel used and range.
Leaves me with 12 other pages to configure
I HIGHLY reco this setup.
it is sweet. Yanked out my analog Speedo and dropped the 400 right in it's place. No drilling required.