I can't seem to find any info about thresholds like max # entities or max map size. If anyone can relocate me or have the answer I'd appreciate it. thanks bob

The map size limits are 32,768 x 32,768 x 32,768. This basically means you could make a half-mile square for you map. You could also give the illusion that your map is 8 miles square with a 3D skybox.

Only if you stick to using the 1/16 scale, you can of course use a different scale (I'm not sure what scale you can go up to)