So you are again going to make something that again will need upgrade?

if you haven't found already that the linear rail choice takes the machine to different category of ability to cope with materials and jobs, too bad.

I am not sure about that gantry and Z design at all. That gantry makes sense with square rails and more importantly made from steel and Z from thick aluminum plates. There are very good other design here at the forum and over internet using round supported rails.

Generally my advice will be - design the best you can , save money and buy the rails and screws, then the frame and slowly build it if money is an issue. Plus life helps you and money comes.

And before you think, hey this guy is a jerk- tomorrow i am going to work for a week something i said i would not do anymore, so i could make some $$ to finish my current build. So its not only you to aim higher.