I started out with a 29g tank and I had two small fish in it.  However, just remember that with proper care, it doesn't take them long to grow bigger, then they will need more space.  So, I would say two fish max.
For a filter, yhou want to get as much filtration as you can as goldies can are very messy.  I like the Emperor and Penguin hang-on-back filters.  on my 30g, I use a penguin 350b and a 150B. 
As for temps, even though GF are "coldwater" fish, they actually do much better in water that is about 74-76 degrees.  So as long as your temps stays in that range, you should be fine.

To me, orandas are the most receptive when it comes to their humans.  They LOVE attention!  However, my oranda that I have now is a big pain in the arse!  He just wants food from me and that is it!  LOL!