1/16" bar seems awfully light for that - think I'd go with 1/8" at
least. While the bar is quite strong in the wide direction, a little
side force and it will twist or bend. I'd also extend it back along
the frame for a couple of the axle screws - get longer ones and use
them to hold the bar on as well.

It may be the perspective, but that big wheel seems as though it might
rub on the boot. I don't know a thing about those skates, but wonder
if it might make sense to make that wheel higher than the others?
That way, it wouldn't interfere with normal skating but would still
guide the skates up and over obstacles when you hit them.

6-32 and 8-32 screws seem way too light. I'd use 10 or 12. The skate
frame may be adequate to hold the threads, but I'd probably use nuts
as well. They are readily available. Loctite on the threads will
keep them tight.

John Martin