Which ram and internal ssd to buy

The non-Retina MacBook Pros have user-upgradeable drives and RAM in all display sizes. The current-generation 13" non-Retina (AKA "Unibody") MacBook Pro is a model that's been essentially unchanged since 2012; it's Apple's only current laptop that uses traditional 2.5" SATA drives and socketed RAM.

RAM: 1600 MHz PC3-12800 DDR3L SDRAM SO-DIMMs (maximum 2x8GB)

HD: 2.5" SATA III (6Gb/sec), 9.5mm thick

This model will accept any 2.5" SATA drive: Standard, SSD or hybrid (a standard platter drive with a particularly large solid-state cache). SSDs are the fastest, but they're also far more expensive and usually smaller in storage size. The largest SSDs I know of are around 1TB (960GB Crucial M500, 960GB OWC Mercury Electra MAX, 1TB Samsung 840 EVO). But they are all more than $400 each; not cheap.

A lot of folks around iFixit have been enthusiastic about hybrid drives such as the 1TB Seagate ST1000LM014. These are a lot more economical, at around $100. I haven't experimented enough with these drives to have a firm opinion yet. Most of the hybrid drives use 5400 platter mechanisms, rather than the faster 7200 mechanisms available in standard drives; the one exception is the now-discontinued Seagate Momentus X series (7200 platter, up to 64MB cache). I currently have 10.10/Yosemite Beta installed on a 500GB/64MB cache Momentus X drive, but as it's being run through a USB2 interface, the speed benefits are hard to see. I'm hoping for a noticeable bump once it's installed on an internal SATA bus.

One option that might make sense is to remove the optical drive, swap the current platter drive into the optical drive slot, and put an SSD in the boot position. That gives you the speed advantage of the SSD, while preserving the storage room of the platter drive. Various retailers (including OWC and iFixit) sell mounting brackets to fit the standard drive in the optical drive slot, often with the tools necessary to do the swap, or with enclosures to use the discarded optical drive as an external USB drive.

Installing a two-drive system (SSD in stock HD slot; HD in optical drive slot) also gives you the potential to configure a Fusion (hybrid) Drive, similar to the stock mechanisms Apple offers in iMacs and minis. This is an SSD joined to a platter drive to create a single finder volume; it gives you far more flash storage than is found in a typical hybrid drive. In normal use, the computer dynamically allocates the most frequently accessed files (the OS, key applications, key user data) to the SSD, while directing less-used items to the platter drive. This means that the stuff you use a lot ends up one the fast drive, the stuff you don't use much ends up on the slower drive, and you don't have to make a lot of independent decisions about what goes where - the computer does it for you.

On your system, you'll have to do some Unix tricks with Terminal to make this happen, but the information has been written up several times. MacWorld's tutorial is pretty solid, and a commenter followed up with an additional trick to recreate a Recovery partiton.

It all depends. How are you planning to use the computer?

Hard Drive Replacement

RAM Replacement

Dual Drive Installation

General observation: When reviewing features on Apple hardware, I personally prefer the standalone OSX/iOS utility Mactracker to the widely-used EveryMac website. I find it easier to find what I'm looking for, since the items appear with pictures, instead of as a text list. Besides, I like being able to get to the info even when I don't have an Internet connection.