Ok, lets start with the basics here;
Depending on the mobo you got its the problems youll get.
If you have a Jasper Motherboard , then its NOOOT that bad, but its still a fat console.
A slim would probably be better, with any type of motherboard.
As for "Mod" the console, you got 2 options.
RGH or Flash the drive.
Flashing the drive allows you to play "Back Up Games" on your system, fats are easier to flash and can be done with items found normally on the house, yes, i did this with normal items at my house. or if you are not techy at all, then get the x360 tools. xecuter usb tools among others. or regular items at your use. and that will do the job. [This also varies from the type of drive your console has].
RGH
Quoting free60:
We found that by sending a tiny reset pulse to the processor while it is slowed down does not reset it but instead changes the way the code runs, it seems it's very efficient at making bootloaders memcmp functions always return "no differences". memcmp is often used to check the next bootloader SHA hash against a stored one, allowing it to run if they are the same. So we can put a bootloader that would fail hash check in NAND, glitch the previous one and that bootloader will run, allowing almost any code to run.
This means, homebrew, unsigned code, games on HDD, dlc on the hdd unlock tools mods, and many many others.
For this, you will need several other tools.
SO pick your needs, and decide which way to go.
I normally would get a slim and RGH. thats always my best suggestions.