Didn't read all the comments in detail, but you will also need a good, sturdy tripod and a remote shutter release if you're going to go longer than 30s exposure.
Sturdy tripod is self-explanitory. You don't have to spend $1500 (unless you want to), and you can always rent.
Remote shutter release is needed because I believe the maximum time for Canon is 30s exposures. If you want longer, you need to use Bulb mode, which means you need to hold down the shutter button. Not ideal, however most/all wired remote shutter will have a 'lock' which lets you keep it open without needing to hold the button down. Or if you get one of the fancier ones it'll allow for an appropriate time without you need to release the button after counting using your watch.
Last, use Mirror Lockup, and ideally the long exposure subtraction which will take a 2nd shot of the same length but without opening the shutter in order to subtract generated noise from the exposed image. Of course, it'll be 2x the length of time.