You absolutely won't need to buy _anything_ :). Free download, free account, and plenty of content. No restrictions in leveling (other than needing to find or buy leveling sigil to unlock each 4 levels), no stupid nerfs to make you worse than VIP subbers or anything like that.
Yesterday my friend got leveling sigil out of nowhere in one of quests we did, at this was just the start of his 4th level - so he can already take his time to level up to 8 freely. I have VIP sub (paying old sub with unlocked everything) and he's doing better than me, so you can take my word at not being hindered in any way.

For new DDO, you just register like on some mmo portal, and jump in to play when the client is downloaded. You can even start playing without whole client downloaded - character maker is downloaded first, then tutorial, then small island you're going to start on, etc. So you can play before the game is downloaded.