It’s unfortunate that you can’t get a little closer to some of the sites, but it’s understandable with the way people treat things (I saw people hanging off of the replica statue in front of one of the temples). They do a great job of keeping this place up though. It’s one of the most well-kept places I’ve seen, quite impressive for an outdoor park like this. There are clean restrooms (some needed to hunted for though) and at least two cafes that I saw. You can find some shade here and there, but in general, you’re out in the elements.
I didn’t look into the guided tours or audio guides, but it might be worth it; the site is huge and sprawling. I’m not sure of the exact size, but if you look at it on Google maps there are sites all over the place; to walk it all while stopping to read all the signage would be a daunting task.
Since it’s such a large site it’s understandable that most people suggest taking a bus or driving to an entrance. Of course, though, I walked from the train station though. on what looked to be a primary entry, but when I was walking back I used Google to guide me from a random spot. It took me through a much more obscure side gate with a site that I have to believe a lot of people never see. Google has it listed as Quartiere Ellenistico – Romana and is a pretty cool excavation.