I have had a bearing holder for my Z-axis made (I cant drill such large holes here at home):
I went to a metal store to buy a piece of aluminum bar (30*10*2000mm). I used this bar to attach the Z-axis to the X-axis. Therefore I also gotten a aluminum plate.
I’m also thinking how I’m going to build the X-axis. I think it is best that I make a metal frame with the guide rails mounted to it. Here is a drawing of what the frame is going to look like: