Steps to open source a small project

I've been working for a couple of years on a small project, almost by myself, with the eventual help of some colleagues. The project is getting out of my hands, because the size of the code is growing (around 20K lines now) and the initial expectations I had for it have outgrown my own ability and time. So now I want to open source it, with the hope to attract some contributors. My motivations for going open source are these:

The project is rather academic (a library of algorithms for scientific computing), and I don't really have any economic interest in it.
The project is getting too big for me to handle it by myself, and the number of features I've planned are enough to keep a small team motivated (I think).
It needs a lot of testing, not just unit testing, but testing in the real world to see if the API is easy to use, the performance is as expected, etc.
I'm sure it has a lot of bugs, but I can only find a few, since its me alone testing it.
It needs proper documentation, because the API is getting a bit complex.

Other than that, I think that the project could benefit from a comunity in terms of deciding which features are most needed, and creating a set of guidelines for the future development.

I'm using Git, so my first thought was to publish it on Github and/or Codeplex. Besides that, what would be the steps to help to slowly grow a community of users and perhaps developers around it? Do I need a domain of my own, or should I stick to Github/Codeplex? How do I set up a platform for collaboration between developers potentially geographically separated? Should I set up a mailing list? And most important, how do I attract people to use it and collaborate with it?

The project is a .NET library for optimization and machine learning, written in C#.

Solution

There is only one piece of advice I can give here; use Github. It is common, (pretty much) everyone knows about it, it is easy to use, and the community who you are trying to attract is already on it. It has a ton of tools which you may not have even thought about, but may come in handy. It it pretty much the perfect solution for what you're looking to do, so don't overthink it.

As for attracting people to use it and contribute, if it is something that is useful and good, people will find it. I have found a ton of obscure projects with a simple google. If someone googles for something related to your project (and it is appropriate named and such) they will likely find it. There isn't really much you can do to force a demand though, just let it happen. As for contributors, people who are using it will likely contribute they're additions back. Just be sure to stay actively involved in managing it (monitoring pull requests, etc). If no one is accepting requests or managing versions, contributors will likely start to give up on your project.