The second thing i to determine where you wanna live and what it costs to live there. Identify a neighborhod and get an address. Take that address and plug it into http://www.propertyshark.com. You then would run a "comparable" for the property to determine what other home sell for. A comparable is a house that s sold with 1/2 mile, 6 months of a similar construction and use. This will tell you what others are paying for for similair houses in the area. You can decide if you can afford the area.
The third thing is to really determine what type of brownstone you are looking for as their are several type to choose from. Goto http://www.brownstoner.com to read the blogs and the forums.
The fourth thing is to determine if you wanna buy something in great condition or something that needs some work.
The last thing is to get your "Team" together. A good honest Realtor, a good mortgage broker or loan rep, a good home inspector and lastly a VERY good contractor. You need these types of professionals if you are doing this for the first time, if you've done it before you can skip the Realtor and the home inspector.
I happen to be licensed as a Real Estate Broker in NY as well as being a Registered Mortgage Broker and a licensed contractor in NYC and Nassau. I carry all these licenses because I buy and sell property and well as build condos and do rehabs for myself and others. Check out my website to see our prior projects. If you have any questions during the process, you can contact me. I charge NOTHING unless I actually perform a service for you. Calls / Emails and advice are as free as air.
Good luck to you
Thanks and best of luck to you,
City Connections Realty