Molecular Cuisine means that you will be working with things like Agar Agar, Xanthan Gum, Gellan Gum, Sodium Alginate, Calcium Lactate, etc.
These are usually very potent, meaning that you will need only tiny quantities to achieve the desired effect, sometimes as little as 0,3g/100g.
So, if for example you want to turn 50g of soy-sauce into soy-gel, you would need only 0,15g of Agar Agar. Using 0,3g would turn it into Soy-rubber which would be inedible.
Your scale must therefore be able to weigh quantities of down to 100th or a gram.
The maximum tare isn’t really relevant. My scale goes up to max. 200g which is way more than I need. For weighing large quantities of flour, suga, etc. I use a normal kitchen-scale.
To give you an idea on the quantities you need, please refer to the linked page which contains a table with dosages for the different additives: