Step 2: What LEDs should I get?
I used red LEDs with a beam angle or 55-65 and an mcd of 1000-2000 and they were very bright. Basically you will want to get the brightest LED you can with a relatively wide angle. A smaller angle means the middle of the card will light up more than the edges while a wider angle disperses the light better. I did find some manufacturers claimed theirs were brighter than they actually were, so you may want to get your LEDs early just to test them out.
Also, and I can't remember where I read this, but I did find a site that basically said red LEDs will burn through the unregulated battery faster whereas other ones will stay brighter longer. I had to install pull tabs to activate the cards soon before the wedding so they'd still be at full brightness by the time of the reception. For some other colors you may be able to activate them the night before and not lose much brightness by the next day. Get your LEDs early and test one overnight to see how well it holds its brightness.