Really it's a try it and see. The 3535 is a larger tractor than the 3616 and overall there is more room, but the variances in the control layout might make the 3616 seem like it has more space for the operator (pedals spread wider and farther away, steering tilts at a higher point).
The 4035 and 3535 are laid out slightly different in the station, but they are the same general size. I could let my 30-35 pound terrier set on the floor between my legs on either the 3535 or 4035, but there is a hump in the floor of the 3616 that would prevent such a thing.
Any of the models mentioned, when equipped with a loader, you
almost need to enter from the left side of the tractor because the loader control on the right side is more to get around to get in. The 3616 I think is the easiest to enter the operator's station and is plenty roomy once planted in the chair. With the 3535 and 4035, while entry is a bit tighter, there is more room once in the seat. I'm slender and 6'2", I have no issues climbing either side of any of them and have plenty of legroom for my 34" inseam legs...
If this were Mexico or the middle east or someplace they have no safety police, you'd see at most 5 people riding on a 3616 operator's station and rear fenders, including the operator. With a 3535 or 4035 there's room for at least 7 with the operator...