Hello Darren,
You have some excellent equipment for CCD observation of variables. For many years I too used a 100 mm refractor. For many branches of VS work you don’t need a filter, so that might be the place to start to see how you get on before buying a V filter.
This includes photometry of cataclysmic variables, such as looking for outbursts of dwarf nova. There is a thread on here about IX Dra at the moment; I use unfiltered CCD for that. Also have a look at the VSS CCD target list which was developed to provide people who are new to the field of CCD photometry of variable stars with some interesting targets to which they could turn their CCDs, whilst developing their techniques. The G filter could also be deployed if you wish. It’s close to V. The only processing you will need for photometry is the calibration you referred to.