I've been making one 2000w element work for my 5.25 gallon batches for the past 2-3 years just fine. A typical single infusion (batch sparge) all-grain day is around 4:30 and likely looks something like this:
Time
(min) Task
0-5 Measure mash water, mineral, and ph treatments...
120v works fine for me. See my response here and you will need a 20 amp circuit.
https://www.homebrewtalk.com/f170/how-many-watts-boil-around-7g-366016/#post4565160
This I seems to be the preffered element
http://bostonheatingsupply.com/SP10868GL.aspx