Pre-order will be enough. There's a case to be made for creating an Imperial crafter because they know their own racial style natively, saving you some gold on the motif book - rare motifs will probably have similarly high prices as on PC when the game launched. But it's pure cosmetics and useful mostly if you plan on crafting for other players.
The world is large, don't worry about this aspect. However, it's more gated than the single player games because each zone has a level range, so while you can sneak into a 37+ zone at level 15 and go sightseeing, don't expect to do any quests. Your level-appropriate zone is big enough to keep you occupied, though, and there are some really atmospheric places to see.
Exploration is pretty good. Not Skyrim level, but still. You can find quests off the road, in random delves, there are a few unmarked ones too. Hidden crafting stations, treasure chests, lore books and skyshards. I actually had the most fun in Cyrodiil despite having zero desire to PvP; it's the largest, most sparesely populated zone, some say it feels empty, but it was nice riding out in the open without tripping over bandits, zombies and what have you every five steps. Just make sure you bring a fast horse... It's even a bit too huge if you try to walk.