Hi, is it possibile to make MT connect to AP and just set DHCP RELAY so my Computer gets IP from server, and to avoid need for another IP for MT WiFi client.

In short, can we make MT to act like a regular AP/APClient, to have some ip from different subnet than the network we want to connect to and then just relay dhcp request to server. . .

Try bridging AP interface with incoming lan interface. It should work, as then any client connected to AP would see whole network behind including DHCP server. I guess you have to use MT 3.x as earlier versions have problems with bridging in such manner.