You can easily add and format any hard drive at 2.5 mm if you get a fatter one it wont fit too well in there. Its easier installing the hard drive before cfw. as for the any ps3 question, any phat or slim model that is at 3.55 or lower firmware can be jailbroken. If firmware is not on that or lower no it can not be done, (Without hardware flasher soldering etc)
If you wish to purchase a ps3 that is capable of being jailbroken or one that already is I can sell you one I have different models available.