Well for starters I would not recomend the mix you have planed...
1. The silver tip shark really needs company as they are a schooling fish. They are also not a true freshwater fish. They tolerate low salt levels when they are young but as they grow older they need a brackish if not marine set up.
Another problem you could run into if you decide to stick with the shark and maybe add some salt is ( I dont know about other people but this is true in my experience ) tiger barbs tend to get sick or die with anywhere higher than .15 salinity.
2. I assume you are talking about clown loaches which also need to be in groups of at least 3 ( perferable 6) and they also grow to be around 8"-12" so not small fish either. They also need a tank with really good water quality and a good current.
3. Why not hook up both the aquaclear 30 and 50? Its not going to hurt ecspecially if you do end with the loaches or either sharks.
4. When you say semi aggressive im guessing you have been shopping at petsmart, now I work there and quite frankly the "semi aggresive community" label is not worth anything. For example we just got in a dozen clown knifes labeled " semi aggresive" if you go by the semi aggresive label you could put things like angelfish, gouramis, tiger barbs, and clown loaches all in the same tank with the clown knifes, not sure if you are familar with clown knifes... basically they are a large (up to 40") extremly aggresive fish that will overpower and eat just about anything else we currently have in stock. Dont go by petstore labels do the research on the fish yourself before making a purchase, because yes most times the employes will try and give you good advice but you could always end up with some new person who does not have a clue what they are talking about.
5. As for stocking ideas maybe try gold, opaline or three spot gouramis. They look great, are hardy as all hell, and are fasinating to watch. Mix in a few larger tetras such as serpaes or maybe lemons for color. Then maybe go with a small school of giant danios the movement they will bring to your tank is awsome. Possable go with a red tailed or rainbow shark... I personally would not as they can drive other fish nuts at times, and grow to a large size.
Lastly, yes live plants are almost always a good idea.
Unless you have large destructive fish, plants provide cover, oxygen, help with nitrates, they help with good bacterial colonization in the gravel, and the look of nice live plants puts fake plants to shame. Get somthing tougher though cus the red tailed shark may damage feathery plants.
Amazon swords are great as with java fern for beginners.
Java fern is also good down the line if you do end up setting up a brackish tank for the shark as it is more reslient to higher salinity.
Hope that helps!
