Wow, that's a challenge.
Strong swimmers.... Once my fry are big enough to eat adult food, they go into bigger tanks with water pumps (full thrust). I use plants and wood to reduce current a bit and as their resting place. They will be tossed around at first, but eventually they will be strong enough to fight the current. But when they're full grown with long tails, they will still look 'heavy'.
To get shorter fins, you could either cross them to PK's or make them grow fast with fatty food (I use tubefix worms) since very young. They will still have the form, but their tails will only grow about half of body length.
Another advantage in crossing to PK's is that they will have thicker/more massive bodies, which IMO would make them stronger swimmers.
I'm not sure what you mean by white copper dragon with orange marbling. Most dragons have white/silverish bodies. It's the fin's color that give them their names: eg, red dragon = thick white/silver scales with red fins. Black dragon = similar body with black fins. etc. My best guess is mixing dragon - metallic - and orange. But still you would need that perfect mutation to achieve the color combo you want.
Betta colors aren't as simple as mixing paint. And mixing genetic codes isn't as simple as it is explained in articles. You need that perfect mutation to get specific combo's, patterns etc. ..... If I may suggest, set an easier goal for starters and work your way through as you gain more experience and understanding.
Good luck, and keep us posted on your achievements...... oh sorry for the long post.