The trouble with the question is that you really need to get an idea of your investing strategy first before you can answer it.
Certainly in some instances it makes a lot of sense to have multiple mutual funds under your belt, simply because it helps spread the risk and therefore minimise the risks while not losing out on the gains.
However, there are some pretty good mutual funds out there which are so diversified they have minimum risks anyway.
Something worth bearing in mind, though - the best performing mutual funds of 1, 5, and 10 years ago are rarely the best performing now - so long as what you're investing in keeps it's head in the top quadrille you're probably doing pretty well.
Also - you should definitely stay clear of funds which overtrade - they are basically doing this to earn fees rather than increase fund value. Definitely a warning activity to stay clear off if known about.
The tax situation really complicates the issue, though - really, you do need that independent advisor and clear idea of their interest in the products their promoting. As before, though, something simple like "investing for dummies" is a book that should help provide a basic but invaluable grounding into the investment world, without overwhelming you with complexities and technical jargon - and reading it should hopefully give you a better idea not simply of what sort of questions you actually need to ask, but also what sort of answers you think you should expect.
Hope that helps.