It really depends on what you're looking for. In terms of gaming an SSD will give you faster load times, fps won't change significantly. Overall, if your OS and any other programs are installed on it, they will boot up faster.
A third monitor is really a personal choice for you, if you think you really need it. Just remember another monitor means more work for the graphics card if you want to play on 3 of them, but you should be fine if your GPU is good enough.