I don't know how many bottles are too many to bring back, but I can tell you this:
I mistakenly thought we could bring back two bottles each so we bought 4.
When I filled out the customs card I saw that it was really 1 bottle each for a total of tw0.
I filled it out honestly (claiming four) and figured I'd either have to toss two away or pay a tax.
When we got to the agent he just added the card to a pile and said "Happy New Year".
Not saying that will happen to others but it happened to us.