will a fair amount (a couple) of fake, real plants limit my goldfishs' grownth?
right now i have 2, 3 inch goldfish in a 20 gallon high tank, without any plants, but would like to add some.

no. if anything, the plants will make them feel more at home, give them places to hide and play

Not to forget that it gets rid of nitrates and puts oxygen in the tank too.

I agree. I have a heavily planted tank, and my fish seem soooo much happier and healthier now that it is... Ive had a goldfish in a tank without any plants or anything, and he didnt do very much and seemed somewhat depressed. They feel much safer when they have plants to play and hide in. LOL, they can play hide and seek in the plants!

Go for the plants, as the others mentioned, your fish will enjoy them

It also makes the tank seem more "alive" and it looks great too.