As far as Google searches tell me, the maximum allowed number of cookies depends very much on the browser, however I cannot find any recent data as to how much cookies are a
The best way would be to not store them in a cookie at all.
Store them in a database, and store the DB key in the cookie. If it's just a few preferences then security isn't much of an issue.
Don't forget that cookies will be sent with every request - if you have 2kb of cookie data and load 10 images on a page, that's an extra 22kb of data.