You would be better off using all West if you can get it. G5 for tacking and 610 for the dropouts. The tacking may not be supposed to hold loads but the demonstrated fail points with their technique is the juncture between bamboo and balsa. Just not enough correct fiber orientation in those spots.
I really don't think their process speeds things up over just mitering, particularly if you have some aptitude with tools. Mitering is a far more secure building method.
You shouldn't have to sand between lamination layers..... no reason you can't do all the layers in one go.
It seems that the BBS goes on the premise that the natural silica layer of bamboo is a good waterproof coating but it really isn't after the plant is cut. Plus every little nick in it is a wick for moisture to get in. Bamboo is very hygroscopic.
I have heard of them using Tung Oil but Tung oil is not very waterproof.
You would be wise to coat the frame more thoroughly if riding in wet weather. In order to do that you have to sand the shine off the outer layer or nothing will stick to it.
Also keep in mind that Epoxy is very sensitive to UV rays so if you don't protect them you can be sure your lugs are on borrowed time if the bike will routinely be in strong sunlight. The Epoxy will rapidly take on a muddy appearance.