I do like watching other peoples' multiboxing videos, so keep them coming. With that said...

1) Scarlet Halls and Scarlet Monastery are the first two really difficult dungeons for multiboxers (or even some solo players) because the mechanics are pretty interesting when compared to other low-level dungeons. Back in the day, people constantly asked about how to approach certain encounters in these two dungeons, so I ended up doing a set of videos showing how I play through them which may be helpful in some areas. (Encounter Explanation / Scarlet Halls Full Run / Scarlet Monastery Full Run)

2) Falling behind in gear while running dungeons with RaF is inevitable, and unless you purposely do something in order to fix that it's quickly going to get worse until dungeons feel like they're heroic/mythic difficulty when they certainly shouldn't be. You mentioned questing, which can help a bit, but if you have the gold to freeze your experience then I might suggest doing that. Maybe research some dungeons (in a similar level range) to see which drop the best blue gear for your characters, and then repeatedly run those few until you've got a good set. It's a tedious way to do things, and constantly freezing and unfreezing your experience every ~20 levels can be pricey if you have no money (20g per character every time you stop and start it), but it does allow you to refine your multiboxing setup a lot better than just simply questing in the outside world would.

Also, I'd say that the first huge wall that you're going to hit when using RaF without heirlooms is going to be WotLK. While transitioning to any new expansion set is going to be rough, when you get thrown into Utgarde Keep for the first time with way undergeared characters, that place is likely going to be a nightmare. Several times I've found myself questing through the beginning of Howling Fjord to gear up my characters so that I could get back into Wrath dungeons.

3) Commentary, in my opinion, is good, and it helps keep people interested throughout longer videos. By no means does it have to be live commentary, and sometimes it's easier to talk over a pre-recorded fight to allow for better explanation of what was happening, how you were tackling it, and how you might expect to fix any errors in the future. Again, not necessary, but you might be able to tie it into some of your HKN tutorials to show others how you made changes to your configuration, and how they helped you overcome certain areas in dungeons (like you did by adding a strafe for your entire team for Commander Lindon in Scarlet Halls).