Oh geez, I hope you end up liking Etrian Odyssey, Chad! Even though there is no reward or incentive for doing so, EO is also available digitally. And there is a demo that is basically the first few hours of the game. You can save your progress, and transfer it to the full game when you decide to buy it, whether it's a digital or retail copy. There is no need to blind-buy it.
I never played the previous games and I don't think I'm missing anything. As I said, there isn't a whole lot of story to it, the game is all about exploring, charting a map, and killing enemies. Very old school, but with many more modern niceties.
If you want to read more about the previous games, I have to recommend Jeremy Parish's various blog entries about them. He's a good writer, and he's very good at communicating his passion for the games he likes. They're spread out on 1up, his personal blog and IGN, so just google him and the game.
edit - Sounds like it's your first 3DS system. Just ask if you've got questions. Some things you'll want to know:
- The XL comes with a 4GB SD card. If you plan on buying everything digitally, you'll want to upgrade.
- You can transfer content between cards simply by copying everything on a PC, then copy to the new card.
- You queue up downloads by selecting "Download Later". The downloads start after you close the eShop.
edit 2 - I don't think you need to buy a retail copy of those games to qualify. It shouldn't matter. Just make sure to register your 3DS and link it to your Club Nintendo account.