Hey, this is promising! Good job.
I am reasonably handy with Excel though I admit a bit put off by the google presentation.
I noted the shield bonus isn't adding up. Easy enough to modify on my copy but I can't modify the master copy, right?
Here's my contribution:
Use the following line to calculate automatically defenses bases on level and attribute
Fortitude
=10+IF(D17>D18,D17,D18)+rounddown(AC11/2,0)
Where D17 is STR modifier, D18 is CON modifier and AC11 is level.
Reflex
=10+IF(D19>D20,D19,D20)+rounddown(AC11/2,0)
Will
=10+IF(D21>D22,D21,D22)+rounddown(AC11/2,0)
With that conditional, you get rid of the need to enter the best attribute modifier and it'll upgrade with level automatically when your stats increase.
With that line, you get automatically the corect fortitude based on level and the better of Strenght or Constitution. Then you add the other modifiers, of course.
For armor, you'd need a check mark to indicate if the armor is heavy not.
=10+IF(*cell with the heavy armor marker*='yes',0,(IF(D19>D20,D19,D20)+rounddown(AC11/2,0))
The most immediate source of improvement I see for this great sheet would be the use of scroll down lists to select class and races. I am sure these list could be used to enter classes and races so that the modifier to those automatically are applied to stats, defenses and skills and so on. That might be a little complex for poor little me, though. The only way that comes to my mind right now is a very lenghty set of conditionals but there are 25 classes and I am pretty sure the formula would end up being too large for the cell (I tried something like that once).