The key thing to clipping is that if you use the average consumer or pro-sumer clippers (i.e., Oster, Andis, Wahl), you have to have a clean horse. Otherwise, you will go through blade after blade after blade.
http://www.amazon.com/gp/product/B003TNTLOG/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1
If you're not showing, see if you can find yourself clippers like these:
http://www.amazon.com/Andis-68035-Progress-Cattle-Clipper/dp/B0018KOI2C/ref=sr_1_sc_3?ie=UTF8&qid=1401495109&sr=8-3-spell&keywords=andish+cattle+horse+clippers
Yes, they are pricey...so see if you can borrow or find some on Craigslist. These are perfect for getting the bulk of the hair off the neck/body in no time and without bathing! I could clip my horse's body and neck in 20 minutes with these. I could then use my (now) Andis clippers:
http://www.amazon.com/gp/product/B003TNTLOG/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1 to do the finer clipping of the legs and head. There are less expensive 2 speed clippers out there by Andis as well.
If your boy has already shed out quite a bit, this second type of clipper is fine as long as the horse is bathed. Buy at least two sets of blades so you can swap out as they heat up. I have found Amazon to have the best prices on blades vs. buying them locally.
Go slow, don't rush. Give yourself plenty of time to work. I like to bathe in the a.m. and clip in the early afternoon or bathe late afternoon and clip the next morning. I make sure to have a deeply bedded (with straw) stall ready so I can take my freshly washed horse there to dry while staying reasonably clean. Depending on the time of year, they will get blanketed with the wicking blankets I have on handed to help speed up the drying and keep them warm if needed.
Use an "approach and retreat" method. I've found my horses (when younger) didn't mind the neck and body clipping much at all once they realized that noisy monster in my hand was not going to kill them. Again, you could get away with just body/neck clipping since you're not planning on showing.
Personally, I can't wait to get that hair off my horses in the spring, so they look like horses and not yaks
So yes, since I clipped between mid-April and early May, I blanketed a few nights as needed. Once we got to mid-May I didn't need to at all. I'm in Maryland so it would also depend on where you are located.
One more thing, if at all possible, find a way to have warm water for the bathing. I am lucky in that I can run a hose from my washing machine water lines (I unhook the washer lines) in the basement. My horses are so much more relaxed during their baths now that I'm doing it with warm water.