BTW, explain the name... Combuctor? All I can come up with is a Deeprun Tram conductor who is highly combustable... I think you might need to get Mikk to make you a gnome mascot here...
As for the custom tabs == bookmarked searches... meh. You can just save searches in a dropdown in the search field, like your browser's recent addresses feature. What I'd rather see is the custom tab be "virtual" bags. You can drop items into it, they'd stay where they are in the real bags, but you could throw, say, all the tradeskill items you actually use in there. The generic tradeskill cat is half useless, and I don't think you're planning on putting PeriodicTable in here, are you?
2. Fubar plugin to display space available / total space
There are plenty of Foob plugins that can do this, there's no reason to put it in a bag addon.
After tinkering, my main complaint is the icon scaling. If I have only 2 items in a filter I get these huge 1" icons. You should set a max size, probably along the lines of 48px (I think that's the largest icon size anyway, any bigger and you're just gonna get ugly scaling).
Something else to consider, one of my favorite features of Onebag is the "bag break"... instead of mushing all the bag slots together a new row is started when a bag ends. You still get the all at once view, but with a small degree of partitioning. This would only be for the "All" view, of course.
Oh and a setting for max columns, Having mostly 18-slut bags I'd prefer 9 cols than 10, that way my bags fit evenly onto two lines each.