The buoyancy issue itself is mostly because of air included as the fish ingests them which is why you should absolutely avoid flakes, floating pellets and freeze-dried foods for fancy varieties. High protein diet can be obtained from Mazuri gel foods (5M70 would be my recommendation here) and Hikari Lionhead. Mazuri can be obtained from Ed at Goldfish Utopia online. I use Hikari Lionhead and Mazuri myself for my orandas, lionhead and ranchus. Bloodworms can be added into their diet. Like other commercial foods, both products I suggested are low in fiber so be sure to add vegetable matter in their diet or make gel foods that compose mostly of vegetables while avoiding ones that are high in sugar and starch. Research online for appropriate fruits and vegetables. I use pear (a little sugary but good in moderation), squash, bananas, carrots, etc.
As for sunlight, I would absolutely not suggest exposing them to direct sunlight. They do not take well to long exposure to sunlight but indirect sunlight is fine. The only difference from lack of sunlight and its presence is the colors tend to be less vivid from lack thereof.
White color tends to stick a lot better whereas other colors don't so your tancho orandas should stick their usual color pattern for a long time although expect some of your fry to have orange patterns splattered around but they may eventually change depending on environmental conditions and genetics.
