Discus and shrimp are like angels and tetra. Most can get away with it, but sometimes you don't. As with tetra and angels, apparently a lot depends upon when each are added, though I have never personally kept discus with shrimp, I know a few people that do...
Filters... Filters are obviously the most important bit of kit in the tank, so you need a good one, and I'd advise building in a redundant system

I run two Tetratec EX1200's on mine, plumed in parallel. A pair of pro 2 Eheims, preferably that claim they can take the tank alone, would both also be good. Depends on the budget. If you have the cash, most will advise the Eheim's, if on a budget, go Tetratec. They are both rated highly on a regular basis, but Tetratec are fairly new (on the market only 3years) do nobody knows how they will preform after this length of time, but at £70 delivered, compaired to an equivilant Ehiem at about £150...... I know which option I prefured, and TBH, Other than the inlet ad outlet sets I'm so far very impressed
Lighting... Arcadia units are the lighting equivilant of Eheim filters. Have a reputation as being the best, and the price reflects that... I use an ebay company called EQJ-trading for all the lighting units that I don't build myself, and they have loads of the things, with different options. They ship from Germany, and arrive within 4 days with so much packaging you can throw them off a 100ft clif and still have a working unit at the bottom. Pain in the A*? to get into though.....
My 4ft luminare with 3 T5 tubes cost £70 delivered. I looked up the Arcadia unit at work, and we can buy it in at £150EX VAT, so I diden't even bother to work out what it would be at retail, and thus the cost to me less my staff discount....
Without plecos, I'd mebe do a bit more reserch into ottos. OK, I had a bad time with them, but I think I may have been an exception to the rule.
Paul has a point. The more discus the better, but I dissagree about the maximum you can have in a tank... 40 in a 80g would turn the poor things into nervous wrecks after 5 inches....They stress at that point when stocked past 1 fish per 5gal at that size IME....
HTH
Rabbut
EDIT to add, the recomended stocking is one discus per 10g
