dear bhai gee
jazakallha for ur visit and thinking me able for ur query, bhai gee i dont have any command on detailing things just trying to learn basics 
for engine bay cleaning i have very good experince with turtle pre-soak, use with 1:5 ratio in spray bottle , work spot by spot means spray solution on one part first than use some brushes for rubbing, scrubbing ( easily available tyer bush, kids feeder brush, long arm brushes ( available at hyper star / metro ) tooth brushes etc ) and wash that area with open water , if require u can repeat the process or go to next part etc
today's modern engines are water sensitive so take care electrical panels to avoid water by covering them by plastic bags etc
sure electric washers better than normal tab pressure specially electric washers with dirt blaster but again u have to take care of electrical panels 