One good source of information - and possibly the hitch if you don't need them to install it - is
http://eTrailer.com. They usually show most of the available alternatives, and in some cases even have multiple photos of the actual hitch, by itself and on the vehicle (which could answer the bumper cap question). They usually have links to installation instructions, which are useful even if you're not installing it, because they show how it fits and let you know what an installer should need to do (so you don't have to believe their estimate). Even when they don't have an instructions link, they show the original manufacturer's part number, and the manufacturers normally have those instructions on their web sites.
Looking for a
2004 Jeep Grand Cherokee, I checked one model and didn't see if the bumper cap needs trimming, but I only looked at one. It should be a pretty simple bolt-on with this type of vehicle, so it is worth considering doing it yourself.
I don't know if I've ever seen a Grand Cherokee without a hitch, so I don't know if anything has to be trimmed, but they certainly look like the bumper cap is designed to work with a hitch.