When the new machine arrives and you first boot it, before, repeat, BEFORE, you create an account on it, it will offer to migrate your data from the old machine. If you do that at that time, and if you connect your TM drive to it, it will move the most recent data from that backup and create an account with your original name, password, etc on the new machine. Once done, you'll be able to log in to the new machine and everything should be as it was on the old. If you don't allow Migration Assistant to do that at that time and go ahead and create a new account on the new machine, if you use MA then, it will not put the migrated files in your new account, but will create a different account and put them there. So use MA when prompted the first time as that is much easier.
Data will migrate pretty painlessly, but applications can be tricky, particularly Adobe and Microsoft products, or anything that uses registration to prevent piracy. You may need to re-register them and you may need to de-activate them on the old machine before you can re-activate on the new. Versions may also need updating to run on Yosemite, so be prepared for working through that process.