looks, good, except the 4 stand offs holding up the linkage arms look really skinny, I would use fatter material to make it stronger… Also you need more weight on the sled I think. You want it around 22-28 lbs depending on frame size. your sled is probabaly around 17 lbs if I had to guess.
and if you will be letting members use it, who might not have a really good understanding of how it works then an emergency stop button is a must.
One good thing about wood linkage arms is they will probabaly break before anything else and are cheap to replace.