What are the limits on this thing?
No idea, if I am correct it automatically hides faces that are not showing. With the system being based around vertex points last time I checked it is more up to the builder to make sure it doesn't use a hell large amount.
Also everything im saying is just based on what I know, I have never used it before and that is the old link to the file. Once you have the bls file as an obj ready for editing I believe the following is not done
No mount points are on it, you need to add them
You need to change the colors to trans so people can apply there own, colors you leave untouched will simply appear that way in game
Textures come applied, not prints. If the build has any prints you need to manually apply it to the objects surface
No testing has been done to see the limit of how many bricks it can work with, like I said last time I checked since its based on vertex count so there really should be no specific brick count. If some one has done testing of the maximum amount of vertexes you can have base it off that. But the simple rule like normal model making for blockland is keep it low for less lag.