As far as feeding Gf goes, a varied diet is a good thing. I've always used pellets or granules or whatever they're being called these days, as opposed to flakes, just because I think that gulping air at the surface for GF can't be good. I've also mixed brands and sizes, just so there is variety. But, real variety is a variety of foods, not food brands. GF are omniverous, so they do like a wide range of foods. I feed mine blanched peas regularly. Take frozen peas, boil them for a minute, take them out of the water and squeeze off the shell. I mince the peas slightly and add them to the tank. Because they have been boiled, they'll sink to the bottom of the tank. My GF love them. My current GF do not seem to like lettuce or spinach (like my last set up), but you can take a clothespin and put a shredded piece of lettuce in the tank. You might have to do this a couple of times before the fish recognize that this is food. I've been recommended to use a piece of zucchini or squash, lightly boiled. I eat so much squash in the summer that I get tired of it and don't buy it in the winter, but next summer, I'll give this a try. You could also e-mail Mighty Queen Pixie, she passed along a recipe for GF food that is gelatin based that you can make. I haven't made it yet, but sometime this Christmas vacation...
As to feeding, it is very hard to do and not overfeed, but if you are capable of it, figure out how much you are feeding for a day. Measure that amount out and give it in numerous small feedings each day. GF, and most fish for that matter, are grazers. I would presume if you can replicate the eating patterns you'd be doing well.
Regards,
Val
