If you've never done this before than a couple dozen pounds is not a realistic estimate.
Dont start from seed,the losses are huge before germination is established,then you've got varmints to deal with,then you have to cull the males,you've got dry spells to contend with,seedlings do not tollerate dry spells even for one week & losses are huge.
If you want pounds & not to be wasting an entire grow season then start from fully rooted clones that are pre sexed,let the clones veg for a week or two then transplant in your patch.
If you want a real idea of what your up against trying to harvest upwards of 30 pounds then watch these 12 videos,its not as simple as planting some seeds then comming back & chopping down pounds of buds,you've got lots of work ahead of you if you really want to pull this off with any degree of success.
This is the 1st episode,you can search out the other 11 parts on youtube.
http://www.youtube.com/watch?v=BXHfkXds0E0&feature=related