Nice! The weather here in the Netherlands isn't much better :P (well, right now it is quite hot, but when I started it was pretty cold). From what I read, is that Avocado plants like "a lot of indirect Sunlight", I once placed one in direct Sunlight, and the leaves started to brown, which meant it was in direct Sunlight for too long.

Right now, I just have the plant as it is shown in the first image (in a big bottle of water, that I refresh every now and then, and re-fill it so the root canal is getting enough water, as long as it doesn't hit the seed itself). You can keep it on water, but you can also decide to pot it with some earth (I have no experience with that, so I don't know (but maybe @trucklife-family knows)).