Thanks for all your feedback! It really inspires me!
I am really enjoying the process. Moreover Alfonso did a great job with detailed manuals. So it is quite easy to figure out how to assemble all parts together.
This is how I made one of side boosters:
https://youtu.be/-PGFpocE9Sg
I finally put the shuttle, fuel tank and side boosters together (attached the photo).
Now I want to make the Pathfinder base and use it as a stand. I want to glue the mission logo under the shuttle and also print the STS-87 crew photo and use it as a background. It should look good I think. Will show you here when it will be done.