Lead isn't a good anode, but lead peroxide is. It's like a car battery, you really need to form the coating rather than just dump in bare metal and hope. A convenient way is just to lift plates out of an old battery.
The resultant solution will be full of lead (and maybe other more-noxious heavy metals). Dispose of it as for battery waste. In theory it's possible to avoid the lead going into solution, but not in practice.
There's a similar problem if you use stainless steel anodes (as I do). However this is _not_ hexavalent chrome (the really nasty stuff) and you can avoid much of the problem by not storing the anodes in the tank when not in use.
This is usually a symptom of excess voltage, or excess currrent density in some areas. This puts too much energy into electrolytic gas generation, rather than de-rusting. It's just wasted energy.
For big pieces, where I can really control the current density by using big plate anodes, then I'd rather run at about 8V or even 5V (5V is a bit low, but big PSUs are conveniently available) Anything over 12V is definitely too high - if you have to use these voltages to get a decent current, then look at providing better anode area or checking the electrolyte concentration.
I don't think this process can be used to remove "significant" rust in under a day. If you try to push it too hard, the chemistry gets bored and goes off into other areas instead.
All "electro-plating" processes are extremely sensitive to current density and to local variations from the ideal current density. Read a commercial handbook for advice here - industrial plating goes to a lot of trouble with magic additives to allow higher currents (and thus higher deposition rates) For the rest of us it's easier just to keep the current down and be more patient.