I found out that
0 has none
1 has one
2 has two
but 3 has none
How many does 4 have?
I believe that 4 has...
...two, if what we are talking about here is common homophones in the English language.
To consider the examples:
0 ('zero') has no common homophones which are standalone words (the prefix 'xero-' doesn't really count...).
1 ('one') has a single common homophone: 'WON'.
2 ('two') has two common homophones: 'TO' and 'TOO'.
3 ('three') has no common homophones ('free' has a different initial sound).
Thus for 4, we need to consider:
'FOR' and 'FORE' - the two common homophones of this word.