Players will be selected for beta based on a range of criteria, including having an active WoW subscription. Opting into beta via the WoW Account Management page is the primary way to register, but other factors, like how long you’ve played the game, may also be taken into account. There will be three stress test periods: May 22-23, June 19-20, and July 18-19. Players will be able to reserve character names beginning on August 13 (or slightly ahead of that time, if you live in the Americas) with up to three reservations per WoW account.
As someone who's leveled enough Alliance and Horde characters to fill multiple accounts, it remains to be seen whether replaying content I've seen many times before will keep my attention in the long term. But even the thought that it might suggests that for many people, this could represent a novel experience compared to the modern game, something at least worth a try.
As you level, you will buy new ranks of spells. If you splurge out on an item upgrade, you will not have enough gold readily available to upgrade to the latest ranks of spells: placing you behind. Moreover, you can buy gear upgrades from the Auction House (AH) or vendors. Furthermore, you may have large investments that need to be paid for professors. You will need to purchase reagents and items such as leather, bolts of cloth, alchemy supplies – unless you have a charitable friend or another high-level alt.