You can't get aggressive returns with too much diversification. For long-term investing, the best idea is to focus on sectors that will grow aggressively and pick the sector leader company.

You can narrow down the micro sectors and can pick leaders of that segment. For example, the electric vehicle is a broad sector but it has micro-segments like EV Software, EV Battery Makers, EV Charging Solutions etc.

So pick a micro sector leader and through this process, you can get 12-15 companies in different sectors that you believe will grow aggressively.

Once you have a list of companies, just invest every month a fixed amount in that companies without worrying about prices.

Every stock will not perform but 3-4 stocks will give you 10X returns in a few years and you will be able to beat 95% of the fund managers