I bought these two years ago and put them in this pot. There's more of them now. Will they sorta reach an equilibrium with the space they have on their own or do I need to thin them out?
No, they won't 'sort themselves out', you'll need to split and replant them in different pot/s, but the time to do that is around September, when flowering is over and just before or when they go dormant. When you get round to it, have another pot ready so you'll have two pots to put them in, or decide where in the garden some of them will go first. Soak the pot to make dividing easier,then turn out the contents and split the bulbs apart with your hands. If the soil is not wet enough or you can't break the clump apart, try running a hose over it to flush away more soil. Discard any bulbs that look diseased or shrivelled, then replant some in new potting soil in pots, or plant in the ground. Guidance here on dividing, but it talks about lifting them from the ground, although the rest of the advice is applicable to your circumstances https://www.gardenguides.com/90764-divide-asiatic-lilies.html