A Quad core would be sufficient from what you described (parts I deleted from the quote). Even a refurbished 2009 would suffice, unless you want to get the 3.33GHz model, and run 1333MHz RAM (as it stands, the 2009 systems would keep the memory at 1066Mhz, even if you install 1333Mhz).I'm thinking that a hexacore may be a bit too pricey and that a quad-core will be enough. And perhaps I could improve performance with an SSD at the onset and then over the next year add more RAM.
As it's not a business system (earning a living with it), then getting your upgrades 3rd party makes more sense (saves on cost, and if there's a problem, though a PITA, you can still manage to deal with getting warranty support from the manfuacturer/supplier you acquired it from).