I do it just about the same way as you. I bubble when I finish a page no matter what, so after a full game in LG, after a page of questions in LR and after a page of questions in RC (even if there's 1-2 questions on the same page as the passage, I do them as a separate page). When I get the 5 minute warning I bubble in all the unanswered letters with the "letter of the day," which is usually C/D, then work through the remaining problems and change the answers if I need to.

The only issue I run into with this is that I sometimes bubble two answers into one line, the last answer I bubbled in for one page and the first answer I bubble in for the next page. If I realize I'm making mistakes like that or rushing too much, I change to bubbling in one or two at a time to keep myself on track.

Most schools will accepted no more than 4 LORS, from what I can tell. Others have a no more than 2 policy.

You should waive your rights because that ensure to the ad com that you did not have any say in what was written in the letter - that its really an objective evaluation of your character/capabilities. So yeah, you don't have to, but you should waive your rights.