My hard dirive broke ¿How should I fix it?

Hi everyone!!! So i have this mac book pro (2.5 GHz (Mid 2012) MBP Unibody 13") and it does not boot cuz his hard drive is broken, so i get a blinking question mark folder when i power it on. Recently i saw a few videos that show how to change the drive . Im looking foward to change my broken drive for a ssd drive and upgrade my 4 gb of ram into a 16 gb ram and also change my old hard drive cable for a new one. I have varios questions: ¿Once I install my new drive it will let me install the os from the recovery sistem?(because i do not have a copy of my old drive, i been booting my mac from an usb).¿What OS should i install?¿What drive and ram and cable do i buy, whats the best one?(Im thinking of a 250 gb ssd drive, i dont need more space).Thank YOU in advance :)))) . Peace!