...and I'm wondering if such a difference between the wrist and ankle is
plausible, before I try making a final version of the tree dino.
I don't quite know what you mean... it's not just plausible but normal.
Partial fusion between fingers occurs in gibbons and sloths.
However, the topmost one in the climbing sequence is going to fall over, and
the hand bones are unrealistic (normal is 2 bones in the thumb, 3 in the
index finger, 4 in the middle = outermost finger), as is the symmetric shape
of the hand (small thumb). And you managed to beat the word _pygostyle_ into
an unrecognizable pulp, I think. :-)