As far as bottom feeders I know they get along with different corydora's. Mine also get alonge with Bristlenose Plecos and my prized Blue Phantom Pleco as well as my Dojo Loaches, Harlequin Raspbora (schoolers), a couple of Tetra's I have (I don't have enough to school), and a school of Cherry Barbs - but I had issues with a couple of long finned zebra striped danio's. Two of them out of a school of about 7 first killed one of my dwarf gouamis by eating off all his fins - he was a very passive Gourami as many of them are. Then they started killing off their school mates - eventually I was left with two danios and removed them to a small tank, then later accidentally killed one myself so there is one left. To keep him company I added Rasdora's and they all get along great. They are pretty accommodating on ph and water temperature - I've never really worried about water hardness since I can't do much about it. Our city PH is so high (8.8 to 9.9) that I have to bring down the PH to about 7 before adding fish but right now I have a tank sitting at 6.0 and they are all doing fine.
I believe any fish labeled "peaceful" will be fine with these guys - they don't even get into skuffles over food with the Cory's they just stay out of each other's way.
Some Gourami's are labeled "semi aggressive" , so you might want to avoid those, although I have a couple I got by accident (the shipper shipped the wrong fish) and other than chasing other Gourami's away from food I only occasionally see attempts at nipping - none have been successful but I keep my eye on them during feeding time,
Gourami's are very slow moving so some might think schooling fish would disrupt their day but I remember before my danio's went psycho they appeared to watch them a lot as if they were entertained but it could have been looks filled with hate LOL - I'm not too good at reading fish emotions yet. A new Gourami will likely be shy so it's good to provide some floating plants - but make sure they have access to the open air - they actually breath air and must have a way to get to it periodically
Does anybody know how Gourami's sleep if they need access to the air all the time - I've gone in there at night but have just succedded in waking everybody up so I've never observed their sleeping patterns,
I'm a hugh Gourami fan and well over 3/4 of my fish are Gourami's. Some dwarf varieties are said to carry disease but I have about 5 different dwarf species and have yet to see any disease.