Insert formulas & copy them to variable size rows and columns

I have being struggling with this over 4 hrs. Could you please help me?

In "D3" I would need:
1) Sum the values of the range "E3" to the last column to the right. The number of accounts changes every month.
2) Copy the formula down to the last row (the last row changes every month)

In “E3” I would need:
1) Type in the formula that is in “E3”
2) Copy that formula to the last row and last column (the last row and column varies month over month)

Thank you in advance for your assistance,
DPP