Queries Regarding Taxes

Hello all learned members, I have some basic queries regarding taxes which happens in practical scenario . so I need the advice of learnned members who have practical exposure of taxation in industry.

My Questions are-

1. where we make the provision for taxes ? in pricing procedure or Taxes are applied during billing/invoicing .

2. If I sell services and product together to one customer then tax rates would be different for for both of them. like for example in india service tax is 10.3 % and VAT is 4 % . so do we need different pricing procedure for this?

3. taxes are applicale on base price or price after discount ?

Thanks & Regards-

Abhi