Hi Idle Di, and welcome from another Upstate South Carolina quilter!
First, that is an ADORABLE pattern!
Second, one of our favorite says here is "there are no quilt police". That just means that if you want to modify a pattern for YOUR use, go for it!
Thirdly, as far as cutting your borders, I would definitely measure both the width AND the length and average that out. As MadQuilter mentioned, if you just sew a long strip and then trim it, you will most likely get a wavy border, and that is NO fun to quilt.
Lastly, as far as your question about navigation...
Your question here is in the "main" area. That grows constantly, so you will probably notice your post changing it's place a LOT, because the "most recently posted response" is always at the top.
Then there are sub-areas - the Challenge area, the section for Vintage Machine enthusiasts, and so on. Posts on those sub-pages act the same way as the main page - the most recent post to have a response is at the top.
There are also areas for files, swaps, "for sale" and so on.
Just take your time, and look around. There's a lot to see and learn. And everyone is friendly, so don't hesitate to ask a question if you need help.
Again, welcome to the Board.