You can prepare items for your death knight so it can turn in quests right away, as some quests don't actually require quest items. This is because some quests require items that you can farm in the open world for easy purchase on the free auction house (If you want rare wotlk items, you should use WoW Classic WotLK gold to buy them. When you reach level 58, the XP for these quests is completely nerfed, as they are technically low-level quests at level 50. Most people will actually leave the starting area at level 59 before the patch because of the XP buff. By then if you turn the Leopold quest, you'll get free XP, which isn't really worth it. Since most of the best beers will advise you to go to the Blasting Lands later, you can even go as low as a 60 down to a 61. Back then, they wouldn't actually offer XP, so it wouldn't work.
You can go and get those items when the XP buff is not active. If you reach level 58, you can still get 12k exp, but the requests in the light tote chapel are more interesting, as there are no buffs over 50k, you can easily lock them down by being friendly with the Argent Dawn. All you have to do is a few quests, like the cauldron quest. Another thing definitely worth doing that offers a truckload of XP is cloth turning in every major city. It's only really worth doing if you don't manage to port you around. If you want to sweat more, you can go to Shilla first. Because when you unlock scenario expeditions with a friendly reputation, you can get tons of free mission turns. But it's not worth doing unless you get someone to summon you there.