You don't want to be washing too frequently, as said above, you will strip the oils out of the horse's coat.
To prevent sweat bleaching, I always hose or sponge off the sweat after a ride just with water.
Rugging will help hugely to keep his coat clean in between washes and rinses.
In regards to clipping, this is not something that is as regular as grooming or bathing.
I only clip my horses coming into winter, if I plan on working them hard and 5-6 days/week over winter. Clipping take away the horse's insulation in winter, so you need to be extremely mindful of being cautious with your rugging. Invest in a quarter sheet to keep the back, particularly loins, warm when warming up under saddle, and avoid leaving the horse uncovered for long periods in cold weather. Clipping is really a pain in the backside to manage, so I wouldn't clip unless I REALLY had to.