A: I believe it's 29"
A: Yes. You may want to make sure they attach to one of the interior studs of the door so the screws do not pull out. Alternatively, you could mount a piece of strapping or other solid support in the locations where the mounting screws will be located.
A: Yes, but the door would likely not anchor with too much strength to a hollow core door. You might look into some supports you could use by bolting them to the door as an underpinning.
A: Yes they can be attached to the size table you are trying to make. I would cut two 12" by 12" attachment plates of 1/2" plywood at a minimum for strength for the slab to protect from the screws from pulling out from use. You can glue and screw the plates or drill countersunk machine screws and bolt the plates to the bottom of the table.
A: Yes they will. The attachment plates are 11"by 11" (appr.) The legs are 24" wide, so they would protrude beyond the width of your table. Also, a glue and screw of two 12" by 12" 1/2" plywood plates, would strengthen the table to avoid the screws pulling out of the hollow core from use.
A: Well, there were a couple downfalls. No instructions came with it. And the wood screw weren't adequate enough for heavy duty legs. I had t
A: There are too many factors to be considered for a good answer. The main factor is top they are fixed too. and the distance between the legs. I installed three legs on a 10' 3/4" 42" wide plywood top. I haven't tried but I'm sure it would hold my weight. (225lbs)