Need advice with creating a company based on open source software

Dear hashnoders,

I'm asking for pieces of advice. You see, for several years I developed an open source software that is now used by hundreds of companies/universities around the world. It was kind of a side thing from my job, but it has now grown a lot! And feature requests are raining.

The time has come where I want to create a small (individual) company (easy to do in my country), so that I can sell "pro support" or "managed solution" (where I host the service instead of asking users to install it on their servers). I'll keep my full time, non dev job too. It'll be a secondary activity.

I would love to get feedback if some of you already know about a similar adventure.

And the big question is: Is it reasonable to ask something like 3k € per year for some custom development on the software and pro support? I already have a "customer" with funding from a grant dedicated to such thing. Would it be better to make a quote for individual features instead of some sort of flat rate/year?

Any comment is welcome :)

If it's relevant, the software can be seen as some sort of specialized CMS. Think Wordpress, but without the bad code part :p

Cheers, J.