Suitable Tropical Fish For A Beginner?

hi welcome to the forum 

as for recomendations on fish it depends alot on the size tank and water conditions , soft  , hard etc

I would stick to the "bread and butter" fish, the common and easy ones such as tetras, barbs, danios, corydoras, rather than the more exotic ones which usually require more care and are more likely to have problems. I'd also avoid livebearers which seem to often have health problems. With these easy care fish you needn't worry about your water, unless it is extremely hard or soft. They will all have been captive bred for many generations, in a wide variety of water conditions, and only those with a wide tolerance will have survived to breed and pass on this tolerance. When I bough second hand tanks,  I inherited  neon, cardinal and rummy nose tetras, all of which live perfectly happily in my fairly hard and slightly alkaline (pH 7.5) water, with no problems. They were kept in similar conditions by previous owners, all local and with the same water as me. I know that these fish are between 3 and 5 years old and look like they have a good few years in them yet. But still people write that these fish must have soft water. Maybe when they were first introduced from the wild, but not now. Unless you want to keep specialist fish such as Malawi cichlids or discus, I don't think water is as big an issue as is often stated.

Remember, choosing fish is like choosing your partner, if you go entirely on looks you are likely to be disappointed in the end. 

Cories grow from 1 inch/2.5cm  to 3 inch/7.5cm depending on the species. Which would be suitable for your tank depends on the size of the tank, in particular the footprint of the tank (width and front-to-back depth). They are a bottom dwelling type of fish so the size of the tank floor is important to them.

As for other fish, again it depends on the tank volume and length. Some small fish are very fast swimmers and need a long tank rather than a tall narrow one. Some bigger fish are slow swimmers and don't need a long tank.