the sand is normal, rust as well from the sleeves. I do suggest dropping thecoolant ratio. No need for a 50/50 mix unless its going to be out in freezing conditions sitting. The more water, the better it cools. I suggest Justice Brothers Super Radiator Cooler with only 20% "coolant" for corrosion protection.
The brakes will have a little chatter, but you can reduce this by ensuring the rotor buttons are squeaky clean, and use ceramic brake lubricant on the back of the brake pads etc.
Also with new brake pads, they need to be properly bedded in. It does make a huge difference.
a good indicator is to walk the bike slowly backwards, then snatch the front brakes. If you don't feel and hear a LOUD click as the rotors shift, the buttons need to be cleaned.