Yeah that model looks like you can do both the HDD and the RAM.
For the RAM in theory some architectures have better performance if the RAM is put in pairs (or threes in some cases), but I don't know if this particular model has that, and in practice the performance boost is barely measurable.
So I'd probably go with whatever's cheaper.
For the SSD, the problem is with the latest version of OSX Yosemite it don't support TRIM (which keeps SSDs fast as things are deleted) for 3rd party SSDs. There's a hack for it but it significantly impacts the security of the system.
http://www.cindori.org/trim-enabler-and-yosemite/
So you either have to go through that, or pick an SSD that has robust garbage collection built in so it's not impacted much by having no TRIM support.
I think the best ones for that are still the SandForce based ones, so an Intel 530 would work. The Kingston V300 and HyperX ones are SandForce based as well.