Before you pay 20% on dividends you have to pay first the corporate tax (21%?). Companies have to pay taxes too. So you have to add up both.
21% corporate tax and then 20% on dividends. So total taxes will be 36.8% plus social security.
About the incertainty of Monaco. You have incertainty everywhere if taxes are low. Even in Latvia, Romania and Bulgaria. Even in high taxed countries you are not sure about taxation next year.
About doing the administration yourself. If you create a LLC in a taxheaven but stay and live where you live normally, so not in this taxheaven, then you will be taxed in the country you live in and not in the taxheaven. Reason is that the LLLC is managed by you from another (higher taxed) country, which is taxevasion. In reality the company is managed from in Germany, so the only reason for going to Latvia was taxes. This is a general rule in almost all of Europe. If they tax you the rule is that you should prove they are wrong. They don't have to proof anything, they just tax you and then it is up to you.
So if you live for example in Germany and have a Latvian company that you manage from your home in Germany, you will be taxed in Germany on the profits from this Latvian company. Unless you can hide that you own this Latvian company. But then you cannot use this profits as official money.