Are you using the small ones or larger ones ??
Only reason to put a leader on, would be if you had a jig trailing behind the crankbait. I use this setup to troll for Hybrid Stripers & White Bass, and put the leader on the front hook eye, rather than the back hook eye. This helps keep the Tot running right, as a back hooked leader/jig will cause the Tot to spin (if you get up to any speed).
I wouldn't add any weight, unless I was "pushing" the cranks (trolling spider rig style, out the front/sides), or unless longline method required too much distance behind boat.
Speed of boat vs length of line out will determine depth. If no one has a formula or answer to your question, here's how I'd figure it out : get boat to speed wanted - run over a 15ft bare bottom flat - let Tot out slowly until it starts hitting bottom - mark line just in front of reel. (you can also measure the length of line, on that test pole, so you can set other lines at same length).
... cp