Of course you'll first have to decide what kind of clothes you would like to make. The process for conforming clothes is different from dynamic clothing. Then decide if the tools from PhilC aren't good enough for you (you can always use it as a start and just push a few verts around with any of the modeling apps). Using Zbrush at lot of things can be done with a fairly basic set of clothing as a starting point. Personally I would say start with creating clothing with the PhilC tools, then use that to play with Zbrush and only then see what is missing to determine what is required and what application suits you best (after testing them).

Study what other people have done. See for yourself what you can do with relatively simple tools (displacement maps, transparency, textures). Study the use of dynamic clothing (pay a lot of attention to using different groups on the clothing, each group can be a different material or can have different properties).

Most people find that they don't really need a lot of modeling to get what they need (given what has already been made, the tools available and the possibilities already available in Poser itself and simple maps).
Unless you want to make clothing to sell, anything produced with any means that produces a result you like is good enough.