I have an office which is now vacant. I am waiting for someone to buy it and it is locked up. Am I permitted to remove the Mezuzah from there? (I need it for the new office) And if I were to rent my office to a goy should I leave the Mezuzah or do I have an obligation to remove it? Any difference between Minhagim?

If you rent your office to a non-Jew you have an obligation to remove the Mezuzah (Shulchan Aruch Yoreh Deah 291 2). If you plan to rent or to sell your office and in all probability this will be to a non-Jew, you can remove the Mezuzah even now. Otherwise if the Mezuzah is a particularly expensive one, you can replace it with a simpler one and take the better one to your new office (based on Hovat HaDar I 12 n. 50).