TBH your ph isnt that high, so long as you go for tank bred discus you should be fine, messing about with trying to lower (or higher) ph is a tricky business and often leads to large swings in ph which is highly unrecommended. A stable ph is always far better for fish, particularly sensitive species, even if its not in the recommended range, than a ph which is constantly changing.
Many Discus keepers, dont have the exact ph and find no problems in keeping them.
AGreed.
Stability in water quality is far more important to discus than simple pH value. Other water qualities like nitrate levels and hardness are more important (nitrates especially). I would check your local water source for nitrate levels. If they are over something like 10-15 ppm straight from the tap, then you simply will not succeed in keeping discus in there long term ..... unless the tank is VERY heavily planted, as the plants will lower nitrate levels.
It would probably save you a lot of effort by finding out if other people manage to keep discus in your local water.
As for the tank size, then that would be OK for a group of 4-5, but no more.
I hope you are planning on a frequent water change schedule !
i shall post my finidings for you guys too see. Ill do it now infact. As for water changing schedual iv resigned myself to doing 3 water changes a week of around 50L each time. Is this ok? 
