Can I and if I can, how easy it is to get e-residency, open bank account and form a company from abroad (I am from Serbia)? Anyone with such an experience and using such company for a startup?
Once you have e-residency (which takes a few weeks to be granted) opening a company can be done in a day. You will need an official address in Estonia, but there are several companies that offer that service. I used LeapIn, whose prices are very reasonable. They can also take care of your accounting.
Opening a bank account requires you to visit the bank in person (another reason why traveling to Tallinn is worthwhile). It is not guaranteed that they will open the account for you. I visited two banks. The first turned me down because I could not prove sufficient ties to Estonia. Swedbank (one the the three largest banks operating in Estonia) did accept me. They have a very good service. LeapIn was very helpful in setting this up too. Please note that Estonia is working on making the bank account opening process easier later this year (I believe it will make it possible for you to open an account from abroad; but it is not there yet, as far as I know).
If your company is a foreign-operated LLC (OÜ), which is what I opened, and what was recommended to me (I have no employees and reside in another EU country) then the only taxes are VAT, and dividend tax, which is incurred when dividend is paid out. There is no income tax.
Note that the dividend tax liability is of the company making the payment, not of the individual receiving the payment. So, even if there was a taxation treaty between Estonia and Serbia to avoid double taxation, you personally may still be liable for dividend tax in Serbia, if Serbia taxes foreign dividend income. But, here comes the usual disclaimer: I am not a lawyer or an accountant. You'd better check with one!