Hello the arithmetic is simple. My first look at the proposed sailplan is that it is a tad too much.
You have to work with some "knowns" For instance hull length and displacement including keel weight.
Starting from there get the keel weight to 40 / 50% of the total displacement. Work out the practical depth the keel will be. Rule of thumb now as a starter.
Weight of keel in say pounds multiplied by the depth of keel from waterline in inches. Call the answer in inch pounds.
What is the wind like where you sail? A 20mph wind has a force of 1 pound per square foot of sail, this we can use as a guideline. The point at which the wind affects the boat is the centre of area of the 3 sails. If you can't work this out then to be honest don't bother to read on! Not meaning to be offensive but it is pre-GCSE level sums.
The hull will react to being pushed sideways, you said only fore and aft sails, to find out how the hull will react, load it down to the waterline in the water and using a finger push the boat sideways, it will slide off to left ot right but moving the finger and trying a few times you will find a sweet spot where the boat travels sideways only, mark this point. I use sticky masking tape and a pencil.
The previously calculated centre of areas (?) (NB NOT the mast) for the sails should be placed 4% of the WATERLINE length of the boat forward of this point.
Measure the sail area centre height above the waterline in inches divide this into the the numbers you have for the keel (weight and distance to waterline) and this will tell you how much sail area in square feet you can use.
You can have a larger sail area but it will make the sailboat more tender. Likewise with these numbers you can increase and decrease the distances and weights to manipulate where you want to be.
It really is easy and the results are guaranted!
I have used this calculation in the last 4 yachts I have built or restored and it is totally effective. The others were already where the designer wanted them.
You do have some tuning you can do with a few degrees of mast slope or adjusting sail trim.
I do hope this helps, some get by with guesswork but have to have the rudder hard over to stay on course.
regards
Roy