Welcome to the forum!
If you are looking to drop your truck 3.5/5, I would suggest doing a 2.5 drop spindle and a 1" spring up front. With this combination, you will not need to relocate the upper shocks in the front. New shocks would be a good idea that are intended for a dropped truck, but you might be able to get by with the ones you have on there now if they are new.
Going to a drop spindle up front, does require the conversion to disc brakes as well. You can get a disc conversion in 6x5.5 so that it still matches the rear and allow you to use your current wheels. If you have older wheels that intended for drum brakes, they have a slightly different profile on the back. Because of that, it may require you to grind the caliper or run a spacer to allow for clearance. If using later wheels intended for disc brakes, then you should be good. The diagram below will show the difference.
In the rear, going with a 5" spring, I do suggest shock relocators. New shocks should be used that are shorter in the rear. Another good idea is a trac bar that is adjustable. I like the Porterbuilt, since it is longer and offers less side-to-side movement through the axle travel.
McGaughys Drop Parts:
http://www.azproperformance.com/McGaughys-67-72-C10/
Disc Brake Conversion (Includes Spindle):
http://www.azproperformance.com/Pro1...60-72-C10.html
Adjustable Trac Bar:
http://www.azproperformance.com/63-7...c-Bar-Kit.html