Question about target brix and residual sugar

I'm about to start a cider with store bought tree top.

The SG is 12.5 brix or about 1.0505 - 6.7% pavb

I plan on using an ale yeast (wyeast 1968) since I have some I harvest from a previous beer.

The alcohol tolerance of the yeast is 9%

So here is my question:

What is the "rule of thumb" for adding sugar to hit target SG. Also what is the "rule of thumb" for hitting different levels of sweetness when using a yeast with a lower alcohol tolerance?

I'd like to know the answer to this specific senerio but also in general, so I know how to adjust for any senerio ( teach a man to fish)

Or would it make more sense to get the SG up to hit 9% and back sweeten it after its done fermenting?
Thanks

I think it will also depend on how you are going to age it and how you will bottle it.

I wouldn't plan on adding enough sugar to hit 9% and then expect the yeast to die off. If you shoot for an OG to hit 9%, murphy's law says the yeast will just eat it all dry. If you add fermentable sugars to hit 15%, then it might be so high that it stalls or STILL goes dry. You never know with a fruit must.

You could try racking and cold crashing at your target gravity. But then you would need to decide how you are going to bottle it. There's a lot of variables that might cause bombs unless you pasteurize if carbing or use sorbate if drinking still.