Whenever I am building larger structures, I find it helpful to design smaller modular pieces that can fit together to make a larger structure. Maybe you can start with the corners to find a good way to outline the building, and then come up with some variations of tiling wall segments that you can repeat 3 or 4 times across the width of the building. Here are some examples of larger builds from my vanilla world that are just a few modular pieces put together into a larger structure:

I believe pressing ‘t’ also does this.

https://steamstat.us/ shows that it’s down for scheduled maintenance.

The first thing I would look into is installing Sodium, which requires Fabric.