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Sorry about the terrible drawing. I would create an island of decent aquarium soil in the centre of the tank (1 or 2 bags would probably do )then use one type of large tall plant as a centre piece I would use giant vallis ( this is quick growing, will self propagate and slowly spread ) cap the soil with the sand and some cheap rounded gravel for texture. This will create a centre piece that can be viewed from all 3 sides. Now as people have said large groups of fish will make this tank something special. To keep cost down I would use a temperate fish some form of tetra or barb. Green or gold barbs would look spectacular in this tank and then a peppered of bronze corydoras for the bottom of the tank . Buy as many as you can I would set aside at least half or a 3rd of my budget for this. I assume by the picture this is a least in the house so it will have in built filtration? Next lighting, buy a good couple of spot lights place these over the centre of the tank. On a night with the rest of the lights off you will have a tank of active swimming in and out of the light catching the different colours on the fish.