Return averages based on day, week, month and year, from dates in column.

Hey folks, hoping someone can point me in the right direction here.
Currently, if I want an answer to these averages, I am literally counting cells and inputting that number into a simple formula. Would love to automate it.

In the attached s/s, please note the yellow and blue cells.

This s/s is recording daily electric usage (grid tied solar, so the negative numbers are correct). I would like to calculate the following for the blue cells:
Daily Average. Total electric usage divided by the quantity of days that have had their cells populated.
Weekly Average, from Monday through Sunday totaled, then divided by number of complete weeks.
Monthly average, Full months totaled and divided by number of completed months.
Annual average, which will obviously take a long time to return a result, but same criteria as months.

As an aside, unrelated to the topic, in the yellow cell, I'd like to not have to adjust the formula on a daily basis. Because of the simple formula I use, cell minus cell, I end up with a large negative number in the calculated cell that does not yet have a corresponding reading entered. Is there a way to have my total ignore this last cell, which, of course, moves every day?

Thanks in advance!

Brett