Yes fill up the whole continent, no need to do it ICS style, but just so that no AI can sneak in a city ie. 6-tiles-apart cities. Spam colosseums, circuses, take any happiness from religion especially Ceremonial Burials. Initially there will be some unhappiness lingering about, but as time goes it will be definitely be back into the positive. Take the free GAD from Commerce to explore, unlike some others here I definitely disagree with not meeting civs and CSes asap. It doesn't make sense - whatever victory path you need to sell stuff for money, you can exchange luxs to please CS who want it (also for your own happiness), you need CS bonuses, you need RAs to get to the required techs fast and that is even more apparent for a SV.
(and @chazzycat)
Keep in mind that RAs are bugged. I'd advise against depending on them. Actually, I advise avoiding them totally. It's not worth trying to play with random outcomes, and it isn't needed, anyway. I win much better without them due to the bugs.
As I said, I am playing a similar game. I don't need CS bonuses because I cannot have them since I cannot find any CSes on my map. I just found Geneva, but that's the only one I have, and I only found it long after taking over the subcontinent.
Here's the problem with finding CSes. If an AI allies with them and DoWes you, they will DoW you, too. It just isn't worth it until you can lock them in as your ally against the AI because the AI has far more resources than you (and they'll use it, too).
The AIs will find you, don't worry. Actually, the CSes will find you, too, as they send out their caravels.
One other thing I forgot to mention. Do NOT give an embassy to the AI civs. They'll use it to spy. They can't spy if they don't know where your capital is (well, they can't spy on the capital and that's the main target, after all).
I'll also mention that I was the last to found a religion in my game, but I'm still winning and have the happiness boosts that I need.
Oh, one thing about happiness... keep it as high as possible all the time so that you get Golden Ages as much as possible. It might dip, but if you manage it carefully, you can really stay on top of things.
Usually, you don't have a choice. Since you are isolated, you do, though, so you should adjust your strategy to take advantage of being isolated. No DoWes, no religious battles, no waste of gold on CSes, etc. Dominate the tech tree and wonders and the AI will be too weak once they do meet you. I vastly prefer being isolated and no AI interference until mid to late game, but this seldom happens on many maps. That's probably why some people think that exploring and having contacts with AI and CS are needed, but this ignores the enormous downsides to having contacts. At higher levels, you start behind the AI and have to play catchup no matter what, so being isolated is excellent for such purposes.
Or you can go meet them, but be prepared to spend resources (units, gold) as well as have delays in buildings and wonders due to dealing with AI interference. If you're prepared, you can do it that way, too. Not sure if you can be prepared, though.