It has to be greater than zero and even, 6 is arbitrary. The upper limit is derived by overall dimensions and laser properites (kerf and “burniness”) of your material. 2mm is a good baseline minimum kerf adjusted tab thickness for most hardwoods, but I wouldn’t recommend pushing it too far, lest you burn your precious (or yourself) up.
I found out there was a limit and stopped. @rbtdanforth went a bit further I think, and quantified how thin he could go. Am I remembering that correctly?
Anyway, if it were me, I’d build a side, then use clones of that one side to build my pentagons. That way I could adjust the tabs on the original path and modify all my pentagons in one shot. There’s nothing to stop you from using variable width or otherwise more decorative tabs (as these are just non-orthogonal finger joints), so there is a lot of room to play here.