Short answer is yes, use curved if you have the space and stay true to his original design. You will get varying opinions on this, mine no different, but here is why I also recommend staying true to the original design. From a purist perspective if you say you are using a Bean Animal then you need to follow it completely. Any changes to the plumbing (in your case Tee's to straight pipes similar to Durso or Herbie) then there is no longer a guarantee of it being silent & fail-safe. It is as simple as that.
I'm not here to say which is better just if you are using a Bean Animal then follow it. Provided you have space. Space is key. My overflow box is huge but I had my overflow drains set to 1 1/2". So when I went to set up the the 1 1/2" street elbows took up too much space so was stuck. Went back to his page and saw that he had a similar issue but it is ok to reduce down to 1". Once I did that everything is fine.
Yes, you will need the hole in the on the Open Channel standpipe that is curled back over and attached just below the trim inside the overflow box. Use a 1/4" x 3/8" John Guest fitting and 1/4" tubing and it will never clog due to salt creep.
Edit: For reference -
https://beananimal.com/projects/silent-and-fail-safe-aquarium-overflow-system/