Couple questions on hand watering Coco

I'm finishing out the fox farm nutrients I have and I am switching to Jack's fertilizer. When I bought the Jack's I was planning on setting up a reservoir but decided to try out hand watering first.

I'd like to mix up as large a quantity as I can. How long can I leave the nutrient solution in a bucket before I use it? Should I seal the bucket between uses or does it matter?

I know people oxygenate their reservoir water. Is there any reason to do it in this situation?

How many plants/area size?

Its for a 2' x 6' flowering area. Not sure how many plants though. Here is what I have going...really need my new lights to hurry up and come in.