[Ctopher]

Start with the EZ Detail Brush Little & Big brushes. The EZ Detail Brush Go brush might come in handy but I honestly use it more with wheels. Also grab some 5 Pcs Premium Natural Boar Hair Detail Brush Set off Amazon, just the cheap ones that will only be used for engine bay use in the future(once you get grease and oil you should not use for anything else).
Grab some SimpleGreen (get the aircraft version if you have aluminum under the hood) and throw it in a foam cannon. I would literally foam the whole engine bay and let it sit, once the foam dies off power wash it. Then foam again and that’s where the brushes come in, just start hitting everything you see, foam some more and brush, rinse and repeat as many times until it’s spotless.
Now once it’s spotless this will take it to the next level, spray it liberally with something like Meguiar's D17001 Hyper Dressing diluted 4:1 or CarPro PERL diluted 3:1. And when I say spray it I mean spray it, the whole engine bay, everything, just go crazy. You can then close the hood and let it dry or go for a drive. These two will give you a low sheen on all the black plastic, hoses, etc. I have not personally used 303 Aerospace Protectant in the engine bay but just on interior. The other two are water based and I’m not sure about the 303.
Once you do this the next time is so so much easier, spray some degreaser and use a smaller brush to hit the little corners, etc. I honestly just use a spray bottle for touch up, spray and brush, spray and brush moving around the whole engine bay. Power rinse and while still wet just go crazy again with the Meguiar’s or PERL and you are done.

CTopher