If you're gonna stay on the beach itself much, w/ an infant, I'd suggest either bringing your own cabana (pop-up or otherwise), or accessing the beach near one of the populated areas that rent them (but that limits the time you can spend at the beach based on when they rent, and you may want to go earlier or stay later).
Going to the beach w/ a kid is more work than by yourself or as a couple, in case you haven't tried. And the work load doesn't go down much as they get older, at least up until 7, as far as I know. Definitely can be fun, don't get me wrong, but being prepared is a good thing. Sometimes the beach is too hot or too windy, and some sort of cover is gonna be good for the little one and whoever is watching. Remember too, little kids are close to the ground, when the wind kicks up, we hardly feel it on our hairy legs, but their faces and eyes are down there, and they're not gonna like that much. One time w/ the kid at the beach, if I didn't have my pop-up cabana thing, the kid wouldn't have had any place to play coz she needed something to block the wind.
I know I recommended finding a condo or house in an earlier post, but if you do look for a hotel, some have more amenities than others. Some have lazy rivers you and the fam can float down, some have pools to lounge around, some have indoor pools that come in handy in rough weather, some even have kid activities or child watch, maybe not for infants, but just more food for thought later.
If you want some good food, Murrell's Inlet is known for some of the better restaurants, and there are hotels in nearby Garden City on the beach. Both of these are south of Myrtle Beach. There's also a shooting range and gun store right there on that main road down to Murrell's Inlet. Can't remember the name of it off the top of my head, but you'll see the sign on the right if you make that turn off 17 to Murrell's Inlet.
As far as tourist trap buffet's the best one I've been to is the one directly across from Broadway at the Beach (the big shopping center w/ the hard rock cafe pyramid and all that). That seafood buffet is a few bucks more than some of the other ones up and down 17, but imo is the best, tons of fresh crab legs, scallops, shrimp, oysters, etc., and the dessert bar alone is worth going for.
Broadway at the Beach is also a fun time to walk around, especially in the evening after the sun goes down. Lots of bars there, from nightclubs to piano bars, and even karaoke. There are some restaurants in there too, and boardwalks/bridges that take you around the shopping campus, you can feed the fish and watch em climb each other for the fish food you buy out of the container, etc.
Have fun.
Karz
PS if you are a golfer, I can make some recommendations there too...