I'm not sure about the vitamin suppliments except the iodine and calcium. I offer fresh foods, dry greens, and some powdered suppliments that they can choose to eat, but I don't force anything except the calcium in the water. Gouldians are pretty picky, you could put the pair together now, just visually seperate them from the rest of the flock.
You won't be able to tell the sex of the chicks until they color, but you can leave them with the parents until the next breeding season, I do. The biggest reason to pull them out is to set the pair up for breeding again so they don't inbreed.
You don't need any feather growth aids if the birds are taken care of well.
Here is the current reccomended diet:
Fresh foods
Soft food (egg food, high protien foods like mealworms)
sprouted seed
dry seed
and have calcium, powdered kelp, and other minerals that are helpful.
I buy a lot of my supplies from here:
http://www.ladygouldianfinch.com/Make sure to purchase nesting grass and a large nestbox that attaches outside the cage. Have a bath available for both birds. I also have a light next to the cage to simulate sunlight to help absorb vitamin D.
Here are a few older photos of the finches, including young chicks being banded. The ones in that photo are between 3-8 days old.

Here are a few photos I took this evening. I need to clean out the cage and scrub the perches, so please excuse that.

I know the perch is a mess, but here are 3 chicks with their dad. Note the chicks just starting to color up.

I always have millet available for the chicks when they are weaning. I also keep food in a gravity feeder so I don't have to disturb them to feed several times a day, 9 finches go through a lot of food in a day!
Here are some photos of the finch I had to handfeed. It was burried under it's 5 other siblings and wasn't strong enough to get up to feed each time. I took over and it is now weaned and healthy.
These photos will decrease in age.




And a video of a begging finch. It had already been fed, it just continues to beg. This is part of the danger when handfeeding, they don't stop begging when they are hungry! Click the image to open photobucket and the video.
