Dear dad,
I know you need heaps more advice than I can give you. However one thing I have learned in my trips to court, is if you can have your proposals and/or objections submitted into writing before you are sitting down talking to a mediator (do you have a court appt mediator before court?) or the judge, DO IT.
Since you are asking about a responsive declaration, I have only disregarded these rarely, for example; in the case my ex files a motion against me in court, I file a response motion, then he goes on to file a motion in response to mine...thats where I get careful. If its trivial stuff, I have sometimes left it alone. If there are false allegations, I respond with a brief (one to two page) summery/response that I am opposed to the accusations, not in good faith, etc. (then of course I get another one back while sitting waiting for the mediator).
But I would always write something up, a whole science in itself...as to what my wishes are for child and WHY its in her best interests. Again, not knowing your AREA, county...etc...as in CA there are different ways...time and time again I have often (not always) felt like a judge made his judgement based on paperwork...and revisions on our testimony....and with court appt mediators, almost always I got they made up their minds before we even walked into the room. And thats at least 12 times. Different mediators.
The courts like a fair plan and if you provide fair solutions they are more apt to rule for them. Also, keep your writings down to 2-3 pages max, so that the judge or mediator will actually read them. Its OK to have attachments.
I would not have your gf come to court to testify unless its a super heavy decision. I am afraid that may confuse the issues for the court.
They are swamped and do the best they can.
I hope you are very prepared when you go in, having submitted your papers to the court as to visitation, that you are super ready with cliff notes as to holiday/school breaks, a regular forum for parental contact (I recommend email), sharing of school and extracurricular activities regularly, contact schedule with the child (follow given advice), transportation rules, and anything thats come up you think could become a problem.
I have heard one friend subscribe to success that she ALWAYS had a number two back up plan to present in court when she didn't get what she wanted the first time. (Personally, I don't know how she did that...it was in CA so it was probably in our court ordered mediation before court sessions...not enough time in court to do this route).
You can always request that either parent makes no derogatory comments about the other parent (and/or step parent) in the childs' presence.