The trailer's listed weight capacity is 1200 Lbs. So 3 600 or maybe 750 or smaller bikes in track trim should be under the weight limit. Most Liter bikes are very close to 400 lbs curb weight, so you'd have to look at the specific bikes and their curb weights to see if you'd be over/under the capacity limit.
There are holes in the frame for tie points. I used a canyon dancer and two ties on each of the front and rear to keep the bikes securely anchored. With three bikes, the tie points are there, but the straps will be crossing each other. If you look at the manual located at this link:
www.midwestindustries.com/documents/manuals/MC1200.pdf
You should be able to determine the locations of the tie points from the drawing on the cover page. The tie points are the end flanges and the holes in the frame.
Craig