SSD Upgrade Dell inspiron 5559 keeping current HDD
I wish to upgrade my storage to an SSD but I'm stuck. I've done some googling and found that I can use a caddy to change my DVD drive an keep an SSD there. My main aim is to improve performance and use both my present HDD (for personal files) and the new SSD (for windows). So I need to know :
The best suited SSD of 250 GB or 120 GB (int terms of performance and size that fits right into the place)
Caddy compatible with my Inspiron 5559 (Caddy is not important to me. I don't know whether my laptop has an extra slot for the ssd)
Where to keep SSD? On the DVD compartment or the present HDD compartment to get better performance.