Yes, gold coin rings are fun! I have done a few, as well as platinum. 

The Gold Buffalo is 24k (.9999 or 99.99%) gold so it is very soft. You would need to leave that work hardened when it is finished or it would be too soft. I typically only anneal pure gold and pure silver coins once but it depends on the ring size.

Gold Eagles are 22k or 91.67% and alloyed with copper to make them harder. They can be annealed more often and left a bit more annealed when finished.

One issue with gold and platinum is the “orange peel” effect. If the metal is stretched too much or reduced too much an orange peel look can happen to the surface of the metal. It can obscure the detail of the coin a little. Be sure to match the ring size to the coin size. Big ring with big coins and small ring size with smaller coins.

NOTE: Silver is more dense than copper, gold is about more dense than silver and platinum is more dense than gold. So the same weight of the coins will be dramatically different sizes with the different metals.

I would start with clad coins, halves and then quarters and then clad dollars and dimes.  Get to know the limitations of the equipment, the coins and yourself. See how big you can go and how small you can go with each coin. I have a chart of what I do in my manual. I tend to prefer the narrower banded rings. That means larger holes but it also depends on ring size. Larger ring sizes need smaller holes to mitigate for narrowing and thinning of the band. Smaller rings need larger holes to mitigate for widening and thickening of the band.

Get to where you can make many different sizes with clad coins consistently. Then move to silver half dollars and silver quarters, dollars then dimes. The silver quarters are difficult because they like to warp due to the difference in thickness of the metal. I discuss this in the manual. Once you’re confident in silver, move to gold. Once good in gold, try platinum. Platinum is a weird metal. It can be stained with iron when heated and it doesn’t abrade but rather smears so burnishing is the best technique to finish the edges of the ring.

Here is a good video showing my latest techniques with a silver coin:

https://www.youtube.com/watch?v=3LgZvibJ2rE&t=37s