As far as 4 links go, you would want both ends the same. The upper links don't have to be spaced too far apart at the axle, maybe 1/2 inch. I've seen some as far apart as one inch, but it's up to you.

Yah, you want that dual triangulation, otherwise the crawler would turn of it's own accord, when it articulated, without even turning the wheels! NOT a good situation!

On the skid plate....see the three holes at each corner? You want to cut a notch at all four corners, so the link rod end will clear the plate, and attach the lower links directly to the side frame plates with a bolt and nut. That will put the lowerlinks on the inside of the chassis!

3-links act as kind ofa pendulum. The upper link acts as a pivot, and the lower links and axle "swing" from the upper link, causing axle swing when the suspension articulates. Four links swing centrally, like when you rotate your wrist. That is the best way, because the axle won't affect the way the chassis acts. 3-links do, as the driveshaft position "swings", from side to side, when it articulates.

Reducing the articulation will make the crawler crawl better, believe me. I have seen crawlers do gangbusters with as little as 38 degrees of articulation! My own comp rig has only 42 degrees, and if you saw it crawl, you would be an instant believer! Axial makes rubber stops for their shocks, or you can cut pieces of the proper size fuel tubing, to make travel limiters, to reduce articulation.