Also it will take you a lot longer to level in TBC Classic than retail. Far longer.
You level in the Blood Elf starting zone, which will be much longer than Retail, then you go to undercity and move on to silverpine forest or you can go to other zones until you hit 58, then you go through the portal to the higher TBC zones.
I find this useful. The 1-10 and 10-20 zones are like the Blood elf start zones.
These numbers don’t change as you level in Classic and TBC Classic as they do in retail. So you are limited as to which zone you can level in.