Well Kelly, You sound like you are alot further along than most when they start. That's great!
Some of the plants to look for are both Black and blue Cohash, Christmas fern, Dolls eye, wild ginger, snake root, Virginia creeper, Jack in the Pulpit, Rattlesnake fern, trillium, may apple. There should be a much more complete list on the PA DCNR web site.
What type ferns do you have there? Does it look like a fern field under the trees or are they just here and there in clumps? The ones in clumps here and there may be a good sign, The ones that look like a blanket of individual fern stems sticking up are probably bad, New York fern and \"hay scented fern\".
As to planting, I would just stick with the random planting. Unless you plan on covering the entire 2.5 acres in sang, the random is best. If you get too big an area planted heavy then you run into diseases and fungus problems down the road. Spreading the first years seed around will also let you see just where it might grow best on your site. I hope this helps, and maybe some of these others will chime in with better advice.
www.dcnr.state.pa.us/