goldfish tank size

Question
Hello I have a 20 gallon tank.I would like to keep goldfish in it.I really like black moores.Could you tell me what goldfish would go well with black moores?How many goldfish should i keep in my tank?It would be very helpful if you could list a nice goldfish community(containing a black moore i hope!)that would be suitable for a 20 gallon tank.I have a very good airpump and an exellent power filter.I clean my tank,algae scare,siphon etc. weekly.I also test the water and its all good.I have many tropical fish and am interested in goldfish,So i have had lots of expeirence.I am a good fishkeeper!:)
   ps: For FANCY goldfish what should i keep the water temp. at i have a heater i could use if needed.

Answer
Maddi,
I think golodfish should be able to be with black mores. Any gold fish.
I am not that experienced in all types od fish, I am still learning though. So, I would ask someone that is more experienced. Goldfish water should be cold though. Probably about 30 degrees or so. Goldfish are all cold water fish.
And no, I would not add a heater.

Thanks.
BethE.