EDIT: From Blizz's own article on WOW Classic TBC Gold the topic. "On the day of patching, players will be able to open the Battle.net desktop app and choose the game you wish to play: Burning Crusade Classic, or WoW Classic. Both types of games will display your existing characters with the old realm name/s. After choosing a game, select a character you wish to play and confirm. You can use an optional paid-for service to access the cloned character in the two game types if you want to play as your character on both. All you have to do is login as normal and start playing.

Because the copy is completed before release and is released. The characters are all present in Classic which means there's no downtime in the copy if you choose Classic. TBC may cause downtime just because it is not immediately. It can also lead to more characters being copied at the same time. This could lead to the system going down.

Bots will probably make use of buy TBC Classic Gold the boost, making it more difficult for bots. However, if bots were properly controlled I'm not sure the boost would pose any issue. Five of my friends are coming to classic since we all love TBC, and they are only joining due to the fact that they can increase their levels beyond the vanilla levelling content.