A composition of a buffer should depend on your exact needs (a buffer solution for electrophoresis and similar techniques, for dissolving proteins, for preserving cells, etc.) What pH and molarity (molality, normality) should they be of?

For any molecular proportion you can base it on reaction ratios or formulation calcs.

Reaction ratios call for stoichiometric conditions, so choose the smallest molecular weight and divide that value into each other ingredient (& then run proportion calcs.)

Formulation ratios require calculations from molecular weights. As above, if solids just calculate mols each, or if in solution form(s) calculate the amount of mols in a liter and use the concentration amounts each proportionally for the final volume of solution. Try setting it up on a spreadsheet for the mathematical manipulation for the easiest way to understand, as well as get proportions instantaneously. There are a lot of ways to answer your question because it is not that specific. You could mean concentrations of hydroxide or hydrogen ions and THAT is quite a bit more difficult...

As your question is very generally put, I think the mathematical method for modelling could be very useful if your components does not react under the conditions of their formulation in your product

Please read the structural property relationship of your proposed raw materials.