I am currently a 1L and am probably going to transfer. I don't understand why people say you shouldn't be thinking about before you start law school. There is nothing wrong with hoping that you do well in law school and can potentially get into your dream school. I mean it wasn't until after I got my grades back for the LSAT that I started to talk about which law schools interested me. So my take is dream all you want it adds motivation to you law school studies.
On that same token though once fall semester rolls around I would completely stop thinking about transferring. Law school itself will kind of do this to you. Two weeks in you probably will feel so overwhelmed that you believe you don't have any chance of transferring and are just going to do your best. This is what happened to me and I just studied studied studied knowing that this is a competitive process and all you can do is work your hardest and do the best you can do. Law school grades are quite arbitrary but the biggest key is to just work as hard as possible. Law school rewards hard work more so than just being smart.
I ended up #1 in my class after first semester and that is when you should start thinking about transferring again, just long enough to fill out your GULC application. Then get back to doing whatever worked for you first semester (or if you didn't do well change it up.) Come summer fill out those other top 14 applications if you so desire.
I also don't necessary think the costs of transferring are to great. Now granted I am coming from a school ranked around 50 so my situation is quite different. Even being at the top of the class transferring will greatly enhance my career prospects. But being top of the class at a top 25 that shouldn't be the motivation for transferring because in most cases your actual short term career prospects would be the same. You don't really lose your grades, they still go on your resume, they just don't get calculated into your new school for GPA and honors purposes.
However, in the long term, when you are trying to make partner or general counsel or other higher up positions the name of your school matters. It doesn't matter if you made law review or what not but it does make a difference if you attended Georgetown, UVA, Harvard, Columbia, etc. The reason for this though is not just legal profession likes prestige (although it is some of it) it has to do with clients. Huge clients like to see prestige. The law schools in the top 14 show them that. So if you have two completely equal attorneys in all regards for a position but one from Georgetown and one from Boston College, in most areas of the country, the one from Georgetown will be picked.
Anyways best of luck to you and think on about transferring. I go to a school that I would be very happy to graduate from but would be lying if it didn't cross my mind that I would like to transfer to a top 14 before I even started law school. And this is also the time to think about it, not come fall semester. Also, please think that you are going to be at the top of your class. Have confidence in yourself, even though law school is very competitive. Most people will come up far short of that but go into it with the attitude that you are going to do your absolute best and for most people that means they want to be at the top. At least in the end you will know that you did your best and with the arbitrary grading methods in law school that is all you can ask for.