I had the opportunity some years ago to see a few examples in the flesh and it "feels" large, like a truck feels large if that makes any sense.
The dimensions for height, length, width don't really convey the feeling of how big it is. It's approx the same width and height as the FV432 or M113 but the extra 2 metres of length makes it feel like you're standing next to something much bigger than either of those two APCs. I get the same impression when standing next to the LAV-25 vehicles compared to the FV432 and M113 and the LAV is still a metre shorter than the OT-64!
The OT-64 also has a minimal number of things to use as hand/foot holds for climbing onto the roof compared to the above mentioned vehicles. I get the impression that you're supposed to enter through the doors and then use the roof hatches to get onto the roof.
Oh and don't forget that it has metal flaps to cover the headlights, some images don't show that very well and it's not particularly obvious that the headlights can be covered to protect them when "bush bashing".
The engine compartment is located in the centre of the vehicle and completely blocks the front (crew) compartment from the troop compartment in the rear. Depending on the variant, the roof hatch arrangement on the troop compartment can vary quite a bit.
Some good to average info sources can be found online but I've noticed there's often some discrepancy regards crew numbers, some list two while others list three. I'd say that's maybe due to the fact that Czech OT-64s typically had just a pintle mount and no turret and therefore didn't need the third crewie. However it could also be because the third crew member is listed as the gunner and the gun location places him in the troop compartment completely separate to the other two crew and some countries decided that for some vehicles, the gun position would be manned by one of the troops rather than a dedicated crew member. I don't know if this is the case for the various operators of the OT-64 but could be the reason for the number discrepancy.
These are some of the better info sources I've found: -
http://www.army-guide.com/eng/product1067.html
http://tanknutdave.com/the-polish-cz...ed-apc-series/
http://www.military-today.com/apc/ot_64_skot.htm