Regards the questions though.
Yes, wash the Coco again. Always wash everything first. You can tell if it's clean by soaking some in a tub of water. Check the ppm and pH of the water first. If it rises when you put the Coco in then it needs cleaned.
Yes you want to precharge the Coco. Basically just saturate it with a really weak solution. 200- 300ppm . Just a little bit base nutes and some root boost.
Set the Res to 300ppm at pH 5.8. that strength will get you through the first couple weeks with no chance of toxicities.
If the bottoms start going yellow you up the base nutes.
Tops go yellow you up the micro nutes. Mids lose colour and go blotchy or you get rusty spots then you up the calmag . Some need calmag, some don't. Not sure why really. My tap water is only 50ppm and I only use it a few times during bloom.
You'll have to hand water for a week or 2 untill the roots hit the bottom and start drinking from the Res. You'll see it when they hit cos the plant will start growing like buggery.
Don't need to ever feed a Coco plant just water. In the event a flush is needed youd use a week solution. Not just water.
Think that covered all the questions there, if I missed any just ask mate. Always happy to help out