I'm still not sure I follow you... but here goes.
The Remaining Funds % can be calculated by dividing Available Spending by Spending Authority. So on row 3 that would be =I3/C3. This figure plus 'Percent Spent' should add up to 100%.
Possible Funding Requirements: If you are looking to extrapolate existing spending over the rest of the year, then you can divide Total Spending by the number of months which have passed and multiply it by the number of months remaining. However this assumes that expenditure is incurred evenly across the year, which may not be accurate. If you are keen to do this, then you can use a formula to count the number of months automatically. This formula counts the number of months between the start of the year and today's date:
=DATEDIF(DATE(YEAR(TODAY()),1,1),TODAY(),"m")
Therefore you could express the formula like this:
=G3/DATEDIF(DATE(YEAR(TODAY()),1,1),TODAY(),"m")*(12-DATEDIF(DATE(YEAR(TODAY()),1,1),TODAY(),"m"))
Possible Funding Surplus (or shortfall) can be calculated by looking at the result of Possible Funding Requirements and comparing it to Available Spending, ie =I3-K3. If you want to express this as a percentage of Spending Authority, then it will be =(I3-K3)/C3