I would go as low as you need to, to feel
well, keep your bg under
control and manage to
sustain it indefinitely. Which is a really vague answer. I am sorry.
To start with, just pick a number. 100? 50? 20? Do it for 2 weeks.
If everything is working, and you are happy, then add a few grams carbs (say 5g/day) every week until you stop being feeling fine, or your bg increases.
If you don't feel fine, then you need to drop lower. Keep dropping, bit by bit, til you DO feel fine, and your bg is on target.
That is your current personal carb limit.
Then eat to it.
simple as that.
I love very low carb, and my body likes it, but we live in the real world, and why would anyone go lower than they have to? There are a lot of nice carby foods out there, so enjoy them if you can - just bear in mind that blood glucose control comes first, because if your bg is uncontrolled you may be doing yourself long term harm, and that will mean you can tolerate fewer carbs in future. Or you will need meds. Or more meds. Or both.
It is just a question of balance.