Alrighty, but lets say i have done all this, and added a ssd. How can i then "clone" the old hdd's content over to the ssd to work just like it was stock? Cause i want the ssd to contain the mac reinstaller and all the stuff needed to easily reinstall mac later on.
For a start you want to download
SuperDuper, it's free until you use it to 'smart update'. I'd recommend buying it as it has performed flawlessly for years and saved my bacon many times. The initial Clone takes about an hour for 1TB but subsequent clones only update what has changed and take minutes. That's what smart update is.
You can make a boot usb installer for Mavericks, (or wait till Yosemite is released) by downloading from the app store but don't install. It will be in your Application folder called "Install OS X Mavericks". You then use "DiskMaker X" to
make a usb, or SD card, install disk. Basically you just run DiskMaker, it will find the Installer in Applications and reformat the usb or SD card which needs to be able to hold 8 GB's, and make a boot disk.
You then have to decided whether you want to make a Fusion Drive, or have the 120SDd and the internal HDD Separate, I would choose to keep them separate. Load the OS onto the the SDD and run your home folder from there, but put big stuff like your Movie, Pictures, and Music folders, on the internal HDD and link to them.
You can use SuperDuper, to keep a bootable clone of your SSD and also use it to clone your internal HDD.