I believe that the front arb is the same size on the EK4 as on the EK9 (26mm), though someone correct me if I'm wrong as we only have the EM1 in the US. Also, the front bars don't require any bracing.
Yes, the suspension should always be preloaded when tightening any suspension bolts. Get the car up on ramps or use a jack and jack stands as in the video.