I'm planning on doing the same soon and am going for the Samsung EVO 840 (1 Tb), which I recently added into my desktop to replace previous HDD. There are other sizes available at differing prices but these drives have good reviews.
For RAM if you go to the Crucial site for example, it will tell you what RAM you need.
As for speed improvements, based on my desktop performance, the SSD should provide a marked improvement. Win 8.1 starts in seconds with the new SSD.
I'm not convinced that increasing RAM improves speed however.