So soon I am going to be starting the design (using google's "sketchup" program that I saw someone on here use) of the PJ after reading some more. Now I have a question that I have not found (or remember finding) in reading's. It is in regards to lamp placement and frennel focal lengths.

Is it optimal to place the lamp at, or as close to as possible, the rear fresnel's focal length? Or does it not really matter?

Yup, the lamp should be right about at the focal point of the rear/collimator fresnel. Some people have found that moving the light slightly gives them better lighting. I forget which direction they move it, but I think it's forward. So, if your rear/collector fresnel has a focal length of 220 mm you might want to place the bulb at about 215 mm.

Actually, for my standard lens build, I found that aroune 200mm was the "sweet spot"

If everything adhered to theoretical ideals, then you'd have the lamp at the exact focal spot of the collimator fresnel, but things decidedly do not adhere to such norms, so we adapt.