Plants!

Enda,
I have made this statement before, I'm an expert on Plants (killing them off - that is) but until someone comes along better able to advise you I'll tell you that the general rule of thumb is that you start off with fast growing simply grown plants - such as Hygrophilia, Saggitaria and the like. These quickly become established and give you heart to venture into the less-simply-grown plants.
But more of that from people better able to advise you.

Barbs can be a bit of a hazard to live plants, although Odessas aren't among the worst of them.

Discus and Gouramis? - That could work but it would rather depend upon several conditions - how big is the tank?
Opaline Gouramis - and the Golden is only another colour morph - were derived from the ordinary Blue Gourami which can be a bit of a bully, but not always. I have had Blues and Opalines which were meek as lambs and again others be really aggressive...but there again much the same could be said of Discus - down the years I've owned those too with totally differing tendencies.
Let's throw this open to anyone with experiences of these fish.

Sadly you, like so many of us, have witnessed what can happen when introducing new fish into an established tank. Really, the need for a back-up tank for quarantining new acquisitions is a first necessity for each and every one of us...it really cannot be stressed enough.

Hope your new plants do better than mine ever do.

John