
one of the best things I can suggest is something like this site http://www.savannahmonitor.net/
There is a ton of valuable information in there and some of it learned the hard way unfortunately.
1: Every monitor is different but on average you can see 1-2" inches of growth a month, sometimes slower. I cant answer exactly about full length but you can expect a 3-4 foot monitor in 3 years+.
2: A reptifogger is not a good solution to keep up humidity, a custom built wood enclosure with front openning doors is ideal. One of the big things about terrestrial monitors is their need for deep substrate, for a sav nearly 2 feet is recommended. The sealed enclosure along with the deep soil substrate will keep the humidity up naturally without the need to saturate the enclosure constantly.
3: A lot, ideally a young sav will eat 2-3 times a day if given the opportunity. A varied diet of whole prey is recommended, the larger part will be taken up by crickets along with some superworms, horned worms, earthworms, whatever safe food you can provide. The second part of the diet can be mixed between the occasional whole mouse ( size varies by monitor) and other whole items such as shrimp, fertilized quail eggs and even baby chicks when the size allows.
1.1 Black Tree Monitor, 0.0.1 Goulds Monitor, 2.0 Yellow Ackie Monitor, 1.1 Ball Python, 0.0.1 Blood Python, 1.1 Sonoran Boa, 0.1 Kenyan Sand Boa, 0.1 Carpet Python, 0.1 Tokay, 0.0.1 Bibrons Gecko, 0.0.1 Frilled Dragon, 1.2.1 Bearded Dragon, 1.2.1 Leopard Gecko, 1.3 Haitan Curly Tail