Here's my thoughts...
1. discuspaul I think has a guide to discus posted somewhere...read that
2. get some dwarf water lettuce or something to help control nitrates AND to give those discus some shade, which they like
3. realize that if you follow most people's advice you will be feeding the discus a lot of food and often, if you use beefheart it's also a messy food. That being said you're tank may have to cycle again to handle the higher load of fish and waste
4. what temp are you planning? 82-86F, then carefull with plant choices.
5. better to do a 50%water change a week than 5% a day.