All units are connected to the switch via a CAT-6 wired network and the Wired Router (Mikrotik) has the DHCP service.
My previous atempts at seting up the system and setting each unit to create a new wifi network with the same name, encryption and bridge-mode has failed, as the netowork has become unstable, unresponsive or with extremely low throughput.
How should I configure the Airport Express units and the Time Capsule to create a WiFi network named XYZ with WPA2 Personal encryption?
As you said, bridge mode with same name, password and security type. This problem seems bizarre as I have an A1034 Extreme set up to provide a secondary 802.11g WEP network for some legacy devices, which is a similar setup to your own. Are you using AirPort Utility 5.6 or 6.0?