To follow a stream down, or up, you almost always end up at a canyon with steep walls, ie, you have to swim it, dragging your gear behind you if you want to get further past those canyons that block in the camps, at least around Barlow they do. And it's too hard to climb around those, too steep. I've swum them, it's nice, but it's a pain bringing your gear, I guess if you have an air mattress and a big dry bag, garbage bag, to put your pack in, you can do it. Brrr though, will be cold. Terrace creek itself, as the name suggests, is actually a series of terraces, which are cool but very slippery and not so safe to climb up, I did it part of the way but stopped because I thought it was a bit risky to do alone off trail. So you can't easily go down to the main river from Terrace, or up it.
Redwood will be a lot less crowded than Sykes, where the hot springs are. Ever since I heard they poured cement to make permanent pools I lost all interest in ever going to those hot springs again. In winter I don't see Sykes being that crowded, but there will be people there on the weekend, but to me, those hotsprings aren't worth visiting anymore, they used to be ok a long time ago, maybe if you've never seen them check them out, but I'd rather spend time away from that scene, it's not that nice, too impacted. But if you've never seen it, I guess it's nice hanging out at night under the redwoods. If you go to Redwood, there's a cool big spot, just hike in, until the trail crosses the stream, there's some big redwoods fallen over the stream, then hike down river along the trail, which takes you to the last camps on that side. That is not the main trail, it's marked with pink flags right when you cross the creek, and actually heads upwards a bit before resuming the climb.
Don't be too quick to state you're not 'allergic' to poison oak, it's not an allergy as far as I know, it's a resistance you have to it, that you can slowly lose over time, and after repeated exposures. I was just talking to some young guy at the farmer's market who got a massive case, him and all his friends, by running through it at night to prove they didn't have any 'allergies' to it. They hadn't, then they reacted, ie, they lost their resistance. The single best way I have found to finally lose that resistance is to soak in the poison oak oil filled hot springs for a while, which will open all your pores up, then go on the next day. That did it for me, heh. That's another reason I wont' use them anymore.
I never had issues with poison oak until I did, and when I got it, at Big Sur in fact, boy oh boy did I get it bad. Twice in fact, made me stop backpacking for a few years it was so serious. As will you if you keep trying to reduce your resistance by repeated exposures, so I'd stop rubbing that on your face and just work on avoiding it as much as possible, maybe you can keep your resistance up that way.
There are no flat spots along the pine ridge trail, except the campgrounds, and sometimes right at the top of a ridge or climb, there might be a single flat spot. People often massively underestimate how steep the Big Sur mountains are.
Winter is a nice time to go, streams might be high, the logs people lay over them to cross them will wash out after the first big storms, but crossing them is not hard. Watch for ticks too, lyme disease is definitely there.
Bushwacking there is great, but watch for poison oak, and ticks, and make sure to bring a map, and a compass. There's no way to know when you have crossed from one ridge to another, and they are so twisted that you can get lost fast. That's if you are planning to do anything actually off trail, which is so hard in general you'll probably have to stop before you get too far from the camp anyway.
Barlow is a few hours in, depends on your conditioning, call it 8 miles, 4 hours or so, if you can hike at around 2mph, then it's a few hours in. Sykes is 2 more hours in, give or take. Redwood is about 1 more hour from Sykes, give or take. But remember, from Barlow to just before Sykes is a long slow climb, then a quick descent into Sykes, then after Sykes, it's uphill all the way to the top of the ridges, 4500 or so feet. So keep that in mind on deciding where to stop, after the initial climb from trailhead, it's basically rolling up and down, pass Ventana camp trail, which goes down 1 mile to river, a mile you have to go back up in the AM, which makes that a bad choice, pass terrace creek, which there is no reason to stop at unless you ran out of light or energy, 45 minutes from there about is barlow. If you find those time frames roughly matching your speed, then the rest of the time distances should be the same for you. Or adjust up/down to fit.
After redwood is a bit too far for a one day hike in, unless you are in good shape and don't mind doing a 3500 foot climb at the end of your day.
There's a hike / bike campsite in the main campground, pfeiffer big sur or whatever it's called, cheap, and parking in the fee lot is $2 a night, or was last time I paid it. Definitely pay it, people break into cars parked on the highway shoulder.
Have fun, there's really not a lot of options from where you'll go, you'll be on Pine Ridge the whole way, terrace creek trail just goes up to a fire road, that's the only real option from that location.
Should be very nice this time of year, I used to make a point of going during the rains in winter, was my favorite time there.
"Eventually it turned into a couple of downhill switchbacks and we ended up by a small little creek surrounded by redwoods."
That by the way doesn't actually narrow it down any, that description fits all the camps along pine ridge to and including Sykes. The flat spot to your left you passed, no water, is right before you drop down to the Terrace creek camp ground, it's the top of the ridge, and those ridge tops are the only flat spots you'll find that aren't real camp sites. IE, when you get to the top of a climb, and right before you go down, there is often a smallish flat spot that can be used to camp on. Also by creeks there might be one or two spots. However, if the creek struck you as truly small, that was Terrace Creek campground, not a very nice one, but ok if you just have to sleep somewhere to go on the next day. Terrace creek though is only 45 minutes from Barlow, which is much nicer, so as long as its dark and you have headlamps, just go on to barlow.