I think add-ons are usually worth getting, but only if you get at least as many chips as the starting stack (ideally more), and optional if you’ve built a pretty big stack already (ie. will have most of the table covered even after they add-on). No rake makes adding chips more appealing, so it might always be a +EV decision.

As for BRM I think you have the right idea, although you can maybe discount the add-on slightly because you’ll occasionally bust in the first hour. Some players are happy to manage BR more aggressively, but if reloading isn’t an option (or just not worth the risk to you) you’ll want to have at least 50x your highest buy-ins and over 100x your average buy-in, ideally twice that amount.

I’d count the $5.50 + $5 MTTs as ~$9.50.

For rebuy+add-on tourneys I treat them as 4x initial price (so $22 for a $5.50), even though my preference is single buy-in + add-on, just to make sure I’m not uncomfortable the rare times I end up rebuying 5+ times.