In other countries, performing multiple activities in the same company is not easy. It requires a lot of extra paperwork, and sometimes it can get so complicated that it is easier to open multiple companies.
In Estonia, in general, a company can perform multiple activities without problems. The Estonian Business Registry requires you to define the main business activity, but this is for statistical reasons only.
That said, there are occasions where it is advisable to have two companies. This is especially true when company activities are subject to different tax or VAT regimes, such as dropshipping / FBA companies or travel agencies or tour operators.
Let us illustrate that with a concrete example: dropshipping companies. These companies do not receive a VAT number from the Estonian authorities, because they do not have a warehouse or physical presence in Estonia, so they do not apply Estonian VAT to sales. However, companies doing consultancy, design, development, etc. do receive a VAT number.
Therefore, if both activities are performed in the same company, you need to be very careful when applying VAT to one activity and not applying it to the other. This is, in the long run, a source of invoicing errors and problems with the tax office.
To make things worse, in a dropshipping company, if your sales exceed a certain amount in some countries, you need to obtain a local VAT account in these countries. These VAT numbers cannot be applied to other countries, and especially they cannot be applied to your consulting activity.
Due to all these complications for you, and given the low yearly maintenance costs of a company in Estonia, for these types of activities subject to two different tax regimes, it will be necessary to open two companies. If your activities are development, design, online marketing and consulting, you can do all that in the same company. But if you also want to sell T-shirts from a dropshipping supplier in China, or act as a travel agency, it is better to open a second company.