Decide whether it is a family affair or if you would like friends to celebrate with you also. I would recommend invitations- or evites. Also- you could have a potluck get together afterwards- or just something simple as cake. That is totally up to you. Or even gather at a restraunt. I have seen it done all ways. And also- if you chose to have godparents for your child- you dont have to be of a certain religion to do so. We are not catholic- and we dont consider ourselves to be one "religion by name" or whatever. We attend a methodist church- and love it there- but we are not "methodist". Anyway- we are going to have a set of godparents for her. Its more of what you have chosen within your family.
That open house idea is perfect.. I would go for that!
Also- we are not doing a typical "baptism" for her- we are going to do a dedication ceremony... which is like a baptism, but they are not actually "baptised in the spirit" until she has chosen she would like to be baptised. We will dedicate her, to raise her in a chrisitan household (or whatever you chose for your household religion) and to bring her up in the church, along with the promise that the people in the church will love her and guide her- and help her to find what she wants in life. Then, when the time comes, she can chose to be baptised if she likes.
Lots of options. Just do it the way you feel comfortable.