Never stayed at the DVC on HH, so I can't comment on where it is, but we stay in Sea Pines every year and go to pretty much all these places. We'll be there in 3 weeks (yea!), and we plan to check out the DVC this time.
If you're not staying in Sea Pines, you do pay to enter. Harbour Town is back a ways into Sea Pines Plantation, but of course, the plantation is not too huge anyway. You can take the trolleys, but be aware that there are two runs - one back and forth from the parking at the front of the plantation, and one that goes back and forth from Harbour Town to the Beach Club, stopping several places in between (including Giuseppe's). Make sure to ask the driver so you don't take the wrong one.
Parking at Harbour Town is tough at night, but you can usually find something by the restaurants across the street as you first enter - don't worry if you miss them. If the lots are full you'll come back by them because your only other option is to drive into the ocean. If you're there the first week of August wave to me - I'll be in one of the units over the shops in Harbour Town.
We like Giuseppe's for take out, but I agree, it's mostly a small, noisy pizza place. Good pizza for HH though.
Can't remember how much we paid for pony rides - maybe $10? A lot depends on who you get to help you. Once we went, I think they gave our younger daughter a ride for free since we were paying for the other one, and led us around for a long time - well worth it. Last time it was a lot more, and we got to walk around a small square exactly 3 times, no more, no less, thank you very much. Don't think we'll do that again as we can do that at the zoo. When they're older we'll definitely trail ride. But, you can pick up sugar cubes at any grocery and walk or bike up to the pastures and feed the horses, my kids love that. Sorry, I don't know how late they run, but you call to make reservations anyway.
The playground at Harbour Town is way cool. I think even an 8 year old would get a kick out of it because a lot of the structures are built right into the old oak trees. We see a lot of older kids playing there, as well as the little ones. Be aware that it's all in sand, so they'll be dirty if they're little.
There's a good ice cream place in the same strip as Giuseppe's but I can't remember the name. Also ice cream at Harbour Town, but very expensive. And if he's still there (but I don't think he'll ever leave) there's a free children's concert at Harbour Town almost every night of the summer by Greg Russell, who's been doing it for 25 years. Adults might not love it, but the kids really eat it up. You have to get there pretty early for a seat, but you can hear it anywhere in Harbour Town. We usually camp out and eat our ice cream while waiting.
Our other favorite thing to do is to go "alligator hunting" on our bikes. We ride around and count how many alligators and turtles we can find each trip. You can find quite a lot back by and in the nature preserve. You can also go on dolphin cruises, or parasailing out of the harbour. The other things we do I think you would do at the DVC, like swimming, tennis, beach, etc.
Okay, that was long, and I'm going to bed. But pm me with any questions and I'll try to help - we've been going for 15 or 20 years now, scary. And hopefully the "Sea Pines native" will also chime in.