wow, unless you are into some serious 3d type rendering, autocad type stuff, 32GB of RAM is going to be a waste of money, programs written today just do not use that much, 8GB is normal, 16GB if you want better times in Photoshop and stuff like that. But 32? Overkill.
Also, it is not now, and never will be good practice to mix and match RAM sets. Even if the RAM is from the same company, same make, same model, bought from the same store, there is a strong possibility they will not play nice together, and you will be plagued with BSOD at inconvenient times.
Reason for this is kits are cut out from the same batch of silicon. This gives them identical properties, therefore identical timings. Different batches will contain differing impurities, mineral content etc etc etc, so internal timings between those batches will be slightly different to significantly different. The standard 9-9-9-24 will be the same, its the other 20 or so timings that no one ever talks about will be different.
Unless you really feel you need the 32GB, 16GB is more than good for almost all applications. Save your money. Stay in slots 2+4 and you'll be good