Have you done a quick Google on brackish fish and aquaria out there? There's plenty of info!
You have a bit of space to work with so you have quite a few options. You might want to avoid the bigger schooling species however - monos, scats and archers, since they all get pretty large and also, considering the schooling factor, will require massive amounts of space.
Stick to some of the nice smaller species, keep the salinity low-ish and get lots of a few fish - mollies, knight gobies and orange chromides will all mix quite well, and as a bonus you can still do some aquascaping without fear of the inhabitants feeding on the plants.
Plant options are quite limited due to the salt issue, but if you keep the salinity at an SG of 1.003 or slightly lower you can try Java fern, vallis, hornwort, Java moss and Anubias.
Good luck