As with the stocks, a mix in mutual fund asset class is advised to be maintained to diversify the risk factor, but as mutual fund in itself has an exposure to different asset classes say both debt including government bond, securities and equity, you would only add to your complexity as tracking the investment would be rendered difficult.
Also, the performance factor and safety is well optimized in a mutual fund category by investments in different companies of different sizes into different sectors by experts who manage your funds. The best a mutual fund investor can do is to select different fund managers to diversify his risk exposure in this asset class category.
So, at its best, a maximum of 4-5 mutual funds, which have positions in as many as 120-140 stocks, (considering 1 mutual fund gives exposure to 20-40 stocks) can be held by a mutual fund investor as else in the other condition when he has betted on multiple mutual funds in his name he could only be multiplying the count of similar stocks, as a similar stock can be held in the other mutual fund category owned by him. Adding to the total cost by way of expense ratio being incurred towards his fund management.
In order that you reap the most out of your mutual funds, you need to ensure that the intrinsic purpose for such an investment is being met i.e. returns together with convenience. And you continue to track your investment on a quarterly basis. Thus the ideal mutual fund count shall turn out to be not more than 4-5 mutual funds of different diversified categories and being managed by different fund managers i.e. of different mutual fund houses
And be cautious not to give away to the false claims by agents to increase your mutual fund count in the aim of maximizing returns. Also do remember that the idea of maintaining a set of mutual funds to diversify the risk is fruitful only to an extent and aiming more diversification with more mutual funds is just a futile idea.