Modding well i cant really explain unless you give a specific area in which you would like to mod
Flashing: You could play backup games with a flashed xbox your best bet is to use iXtreme LT firmware if you have a Benq or LiteOn DvD drive
Free DLC: you could get free DLC if you have a Jtag not sure how though but it is possible
Jtagged Xbox: You will need a pre-Nxe xbox to jtag it and what this allows you to do is run unsigned code therefore you can pretty much do anything you desire pretty much without boundaries pretty much.
The safest against bricking and banning is just getting it flashed and the best for exploiting is a J tagged xbox