Do I need to lower my forks?

Just keep in that as you change the fork clamp position ie: lower or raise the fork tubes in the clamps, this will directly affect your bikes handling characteristics. The less the fork tube protrudes above the top clamp, the lighter the front end will feel and therefore the higher the tendancy for understeering and washout. And likewise if more tube protrudes above the top clamp you will get the opposite effect. This is not to say you shouldnt alter from the stock settings, you should change it to fit your preferences if necessary, but just keep in mind if you alter this from the stock setting it will affect handling and I would recommend making changes in small increments at first testing it out to see how you like it and go from there. Another way to alter the front end height feeling without drastically effecting the handling is through different bar mounts and bar bends. Just something to think about.

No you can leave them be if it feels comfortable to you. Many of the pro riders will lower the rear end on their bikes by cutting both the seat and subframe without altering the front end, save triple clamp changes, handle bar mounts, and bar bend changes. However, there is nothing that says you cant change the fork height just do it in small increments and test ride each change to see how it feels. Start with just lowering the subframe and seat foam and see how it feels, if it is awkward I would try changing the fork height before spending oodles on new clamps, mounts and bars and if changing the fork height works for you then go for it, but if you find it still doesnt feel comfortable then you will probably need to get the add on parts to change the riding position up front.

shiftmx731, I just found a short article on Transworld Motocross' website that essentially talks about exactly what you are trying to do, it is pretty general information and a lot of what we have already discussed briefly but probably something worth giving a quick read. Here is the link:
http://www.transworldmotocross.com/mx/how_to/article/0,13190,1177923,00.html

If you drop the front end you can always compensate a bit by running some more shock sag, considering you my get 10mm out of the forks you could make up for some of that in the rear without too much of an effect on the linkage ratios