How does investing through Estonian OU works? Any limitations or it's the same process as on personal level?
example: buying real estate in Cyprus / UK / Ireland. Can Estonian company buy RE in these countries without any restrictions?
That's not up to Estonian law. It's up to Cypriot, British, and Irish law. The short answer is that yes, an Estonian company can buy properties there, but there can be restrictions in place for certain properties. Sometimes forming a subsidiary entity in the country of acquisition makes deals easier.