I am a strong believe in a lot of roughage so as much hay as he'll be able to eat!
Because he is 4, I'd personally do 3 days on undersaddle (light) 2 days of ground work/lunging and 1 day off.
Feed wise, each horse is different and if this works for your horse then bargain! If it doesn't you have the fun task of finding what does work (which is what I went through).
My boy is rising 2 (21 months as of tomorrow)
Lunged 4 times a week which includes ground work, lightly.
As much hay as he can get, he does have grass also.
At night -
Protein mix (replaces Bio-mare when I was using that)
Seaweed meal (has just about every vitamin in it)
And he gets a biscuit of lucerne hay with it
It's winter here, this was taken on Tuesday!