Slowrotor,
The problem is much more than just disk loading, which is easy enough to insert into a momentum formula. see this page for a nice summary:
http://www.eng.upm.edu.my/~aao/week2/week2.htm
The typical total helicopter system figure of merit is about .60 or so (a good rotor alone is about .75 to .80 , but the transmission losses and tail rotor lower that figure). This means for 25 lbs/HP you must have about 1 lb/ft2 disk loading.
For this, you must be able to make a strong stable blade that can be this thin. Example, if you want the whole shebang to weigh 250 lbs less pilot, and then accomodate a 160 lb pilot, you need to have a 410 square foot disk, which requires blades 11.5 feet long. The blades might need to weigh about 10% of the empty weight, so they can only weigh a total of 25 lbs, so you must come up (for a two bladed system) with a pair of blades, each of which weighs 12 pounds and can hold about 420 lbs (for a 2 G max structural capability).
The actual challenge is structural, since this thin, high aspect blade must be stable and strong.