Responsive single page website, CSS Grid, SaSS

I found the biggest challenge to this project was getting the complex layout to work on all screen sizes. I tried to limit the number screen sizes I was supporting just because it was getting difficult to balance different sizes. For example I didn't bother supporting horizontal orientation on tablets.

Any advice on deciding on good, reliable breakpoints would be appreciated.

Thanks in advance to anyone who cares to comment on this challenge solution, your thoughts are appreciated!