Ask HN: What to consider when open-sourcing my app?

First, an introduction: Spendful.com is a budgeting tool that lets you track your spending manually. The unique (maybe not?) thing it does is forecast your balance in the future to help you plan better. For those in the US, yes Mint.com is better for tracking spending - but I don't agree with linking bank accounts because that defeats the purpose of developing a habit of tracking where your money goes.

I've realised it isn't good enough to make it as a business in it's current state and I'm not able to give it the time that's required to improve it fast enough to keep up with others. There are ~11k signups so I know some people must find it useful. 7 people pay for premium even though there are no premium features (it did have a 60 day trial as of a month ago but I've since removed that restriction).

My question: What should I be considering when converting an app to be open source? I've made the repo public but I don't have any experience with open source (other than using it) or if this is even worth-while?

- Should the business model change to be free for everyone on the hosted version at spendful.com? - How do I restrict the open-ness of it to just the code and not the brand, design e.t.c.?

My goal is to have people improve it with me, host their own or use the hosted option at Spendful.com.

Any advice would be greatly appreciated. Also, if this is just a shit idea please let me know so I can stop wasting time on it :)