When a CPU is locked, it refers to the clock ratio being locked; the processor gets its clock speed by taking the base clock (100 MHz) and multiplying it with the clock ratio. By increasing the clock ratio (and the CPU voltage when needed) you can make the processor run at a higher clock speed, which is referred to as overclocking. It's a completely safe procedure as long as you use common sense, and even if you don't feel the need to overclock now it might be a saving grace in the future.
Oh and don't worry about the SSD being incompatible with the case; it has SSD mounts built in, and even if it doesn't you can get an adapter for like $2.