At least 8 x 4 GB sticks, but possibly 8 x 8 GB sticks, depending on price. The speed is secondary for the moment, as long as it is 1600+ and the RAM is low voltage (1.35V). Much will depend on price and availability. Maybe I can use the six 1600 4 GB sticks I have and only buy two more, although less than optimal. If anything, my current 1.5V sticks may cause problems when overclocking. I’ll have to figure that one out.
Why consider even 64 GB when 32 seems more than enough? The thought is that the extra price of the additional RAM is small, but the potential benefits are great. One can use somewhere between 32 and 24 GB for RAM cache to improve performance. Is it worth it? Like so often it depends on the codecs you use. If you use heavily compressed codecs like DSLR, AVCHD or RED then yes, it is worthwhile, if you use simple codecs like HDV or DV, no, it is not worthwhile.
There is another consideration to go for 64 GB memory and that is if you use After Effects quite regularly. After Effects has very similar hardware requirements, but it will happily gobble the additional RAM when going from 32 GB to 64 GB, especially with the new Global Performance Cache.