Hi mcdonaldka, and welcome
First question i'm going to ask is has this tank cycled?
I'm fairly new to this myself and so i'll try and explain in the simple terms that i understand to help determine your fish.
What we really need to know in order to properly suggest the correct fish for your community is your water conditions. Fish can't really just go in any tap/well water etc and everybody s water is different. Levels of Kh, carbonate harness, and Gh, general hardness of your water, along with the ph, are very important in determining what fish you can have.
The best thing for determining this is to, if your haven't already, is to ring/google your local water supplier to find out or most display these levels on websites etc.
You could also buy the test kits to determine these yourself.
Once you know these you can determine whether you have soft or hard water etc and therefore determine the fish that are best suited to your water. Trying to do it without knowing these levels can often lead to long term problems with your fish, and can make them quite unhealthy.
As for the fish you have asked about, the Rainbow Shark
- should not be kept in an aquarium of less than 4ft (48 inches) as it will attain a size of 6 inches, so i would guess your tank at 30 tall would be much too small for this as 4ft usually represents at least a 55 gallon. These fish are also very territorial, hence the large tank size requirements and so by putting them into a tank too small you could cause excessively aggressive behavior from them.
The Pearl Gourami
i dont think you should have a problem with, your tank would be about on the limit size wise - i think - and could therefore manage these depending upon other inhabitants chosen and these have quite a wide range of water parameters, so depending on your answers to above, would most likely fit into your tank fine.
Other details you could throw in to help etc are levels of your ammonia, nitrites and nitrates. Do you have a tester kit for these? Or how do you test the water?
What are your tank decorations? Do you use live plants? Any and all details are helpful.