Hello!
To make tap water safe, you need a water conditioner. You need to dechlorinate water before you put it in the aquarium, and when changing water. I would recommend prime, but it is really concentrated, so it might not be for your 10 gallon since it would be nearly impossible to measure it out... maybe something like
Api Tap water conditioner...
As for the fish, that is a little tricky. I would first need to know what filter you have, but you would be
barely able to fit 5 of each. The thing is, you should have at least 5 of each fish species to keep them happy, so that is why I need to know what filter you have, because with 5 of each fish, you would have to do if 30% weekly water changes, but that is doable. Since you are a beginner, I would suggest getting one species first, seeing how they do, learn how to manage water changes etc, and also letting water stabilize before adding more bioload, and then add more fish. Here is a really good site that measures fish cap in aquariums, that I use all the time, and used it to find the info for you:
http://www.aqadvisor.com/ . Just put the kind of filter you have, and add the fish. I find it accurate like 80-90% of the time. I am assuming that you have a standard filter for your aquarium size, like an
Aqua-Tech power filter 5-15, so that is the one I put in the box to calc. the cap.
A heater is almost always necessary when keeping fish, especially when keeping tropical fish. This is because it helps maintain a stable temperature. Most heaters are preset to be at 76-78F. The minnows like water cooler than 80F, in the low 70F, and danios in the high 70F. So I would say that a heater would be good for them, since it is better to have a stable temp. then really cold, fluctuating water temp.
I am in no way a Fish Expert, but I have a couple of years under my belt, So I am mostly talking out of experience. I would appreciate if someone confirmed this info, just so you can have peace of mind.
I hope this helps!