What should I be responsible for as the first developer in a large scale web project?

I am the first developer in a large scale web project, in the real estate sector.
I am not an expert in any field, I know the basic of all, programming, databases, something about design and a little bit about SEO, and website optimization / caching. And I have some knowledge about other technologies and stuff that could be required in the project.

So I am a developer, my boss does some drawing on a paper to present me his ideas and then I start programming and I show him the result. Until now there was no problem, but now the web application is large enough, and it lacks a little bit of database optimization and intuitive user interface. Beside the website, the project also has an offline newspaper, and a desktop application that is a reduced version of the online one, both this things are not managed by me, but by other people or developers that are external to the company.

We do not use a collaboration tool for sharing knowledge between the people working on this project, just emails, and we do not use a development methodology, as for the team, we are:
the developer(me), a designer, a secretary and the boss.

I have the possibility to ask the boss hire the people I want so I can increase the team and have the right person dealing with the right part of the project.

This is the story, the real question is, what should be my attitude towards the project and the company? Should I stay a developer and participate in taking decisions and organizing tasks from time to time to help the boss? Or should I get more serious about this and try to learn project management and implement everything I consider it's required to ensure the quality of the work and final results?

I am the one who best knows what has been developed until now, should I try to organize all the work and the team? Or should I ask my boss to hire some expert to do that?

I hope someone before has been in my position before and can give me any good indications..

Thanks!

From your description the type of leadership role that may make more sense for you is an architect. So you can orchestrate best practices across the different development areas. This type of change though isn't for all developers. Many love being in the code instead of communicating and influencing others. So eveluate what you love.

I think your assesment of needing a project manager is probably a good one but unless you like creating schedules, getting estimates and tracking people down to find out when things can get acomplished I really suggest staying away from it. It really is just a management thing rather then a development thing. Very different type of satisfaction.

Luck.

I think you should be responsible for bringing the beer!.

Jumping into project management simply because you know more about the project than anyone else is not a sufficient reason. Managing projects well is a skill, and if you want to learn how to do that, perhaps reading the book Making Things Happen by Scott Berkun (I wrote a little bit about this book on my site, oddly enough, published this morning) which really goes into great detail about managing a technical project.

That being said, that doesn't mean you shouldn't go into the management side of the project. But if your project is being managed well today (that is, are you reaching your objectives to extend your application, are people communicating effectively, etc), then while you may be thinking about structuring the team a little more effectively, you should not be switching roles.

I would suggest to find someone to bring into the team who has the skills that you are currently lacking and that will impact your ability to build and extend your application. Perhaps initially that person would report to you, but it's not really relevant. As the team grows over time, the person who is most effective at organizing the team will be the one to be the project manager.

Laying the proper foundation from a technical stand-point. Changing technology in the future could be expensive. Make the right choices. Best of luck.