Hi Sonicblast,
This will be a bit overwhelming so please bear with me!
With goldfish, they need plenty of space to swim around and the space is also important in greatly diluting the toxicity of the wastes being produced by the fish. Considering goldfish themselves do not stay small (which is why fishbowls are impractical nowadays) at 8-24 inches range, a general guideline for fancy types should be 15 gallons per fish with 10g per additional fish whereas pond types need 20 gallons per fish. This does not mean the use of individual 15 to 20 gallon tanks is feasible. Those tanks are still very limited and you cannot keep goldfish in isolation as these are sociable by nature and unlikely to thrive for a long time if deprived of their company. With the number of goldfish suggested at two as the possible minimum, a 55g would be a best starting point for fancy goldfish whereas 75g would be the minimum for at least 2-3 pond types.
In my experience which varies I am sure with others, I can never keep my orandas successfully with feisty varieties such as ryukins and comets. I prefer not to mix the pond types (comprising of hibunas, comets, shubs, wakins, watonais and jikins) with fancy types with the exception of ryukins and fantails who can handle themselves very well with the pond types especially when it comes to feeding time.
Be very careful with the varieties you mix. Not all varieties can mix well. Bubble eyes and celestials for instance are extremely delicate fish. With their rather obscured eyesight due to the genetic modification done to their eyes, they tend to be less competitive and are unable to get their fair share of foods when mixed with the more aggressive varieties.
I keep mostly orandas currently. They are kept with the ranchus and lionhead in my 75g tank and have been coexisting very well without problems so far. The ryukins, watonais, comet and shubunkin on the other hand, have been moved to my pond as they were outcompeting the others for food. Hopefully your ryukin and oranda may balance each other's share of food because unlike others, I did not have much luck with that combination. If you opt to add more varieties, avoid the pond types. You could try more orandas or for additional variety, ranchus and lionheads may work just fine with you.
Avoid the pearlscales if possible. They tend to be a little slower due to their rounder body shape which incapacitates their ability to swim with agility thus the ryukin may end up several steps ahead of the pearlies.
Hope this helps!
