When constructing a deck, am I limited to 4 total Raichu, including Raichu BREAK?
Actually, BREAK is part of the Pokemon's name. So you can play up to 4 Raichu and up to 4 Raichu BREAK in your deck.
Source: BREAKthrough FAQ (2015-11-19), TPCi Rules Team (2015-11-19)