Keep going, looks alright to me.
I would skip the area above the rosette welds, that's just me though, sometimes I'm lazy.
Looking at the last picture, it's already stiffer.
Welding the perimeter will make it better of course, I just wouldn't do a continuous weld.
I had the same issue. I used my plasma and cut about 1/4 in or a little more of that lip the entire length. The the remainder of that lip to the portion of the sub frame. Stitch weld it do not make a continuous weld.
Ok quick update, I was having troubles with the lip on the stiffys and fitting to the frame, on the passenger side I pre cut off the that lip, and I must say without that extra reinforcement the stiffy pulled up to the frame much tighter and was more pliable, so not so bad an install on that side. I do wish they cut the notch/angle for where it bends on the frame a little wider so I could actually weld it to the frame rather than fill a gap. Now that they are on not so bad, and it will be nice to incorporate any additional stuff in the future i.e. Long arms, skids or rock sliders.