For testing the water, a liquid kit is best. You can get strip/dip test kits but these don't last as long. I've had my liquid test kit for almost 2 years now and still have plenty left
I use this test kit, which tests for Ammonia, Nitrite, Nitrate and PH.
It's an essential piece of equipment to have. I use mine if Lucky seem's a bit off and I want to check the water quality's okay.
As for a heater? I don't think it's necessary for fancy varieties to have one? Perhaps another member can comment on that.
Plants are always a lovely addition, but be sure to quarantine plants before adding them to the tank. Some times plants can carry certain diseases/bacteria or carry little critters like Snails. So you want to be to sure to be rid of those before adding it to the tank.
I'm out the door for work right now, but when I get back later, I'll post a bit more detail about quarantine for plants
Also goldfish will eat most and any live plants in your tank, as I'm sure you've seen
I've personally only ever had elodea and cabomba.
Okay so quarantine, there are a variety of ways to do it, what I personally do is when I get the plant, I'll rinse it in tap water and look for snails or any little critters, I have a nano pond tank so any critters I find get put there. But you could kill them if you didn't want them.
Then you can soak the plant in a salt solution for about 5 or 10 minutes, I'll have to try and find the exact amounts I used..... then I'd rinse the plant again and soak it in water for a few days, changing the water out each day, just to make sure there's no salt. Then I'd add the plant to my tank and as I have a UV bulb on in my filter I'd flick it on for a little while, just in case.
Hope that helps, will try and find what the solution of salt was....