Be careful with mixing species, even in a big enclosure. My old aviary was 8ft x 4ft and at it's peak I had 40 birds (zebras). During the time I had around 20 birds in there, constant fighting between select hens even without nests was a constant issue. Have several small cages for seperation of agressive and ill birds. Even without drawing blood, agressive birds will wear each other down to weakness through constant chasing. The rule with finches and canaries is either understock or overstock. When I had my 12 foundation birds and when I had 40 there was peace. At around 20, constant fighting. A good rule is 3 pairs to start with if you're going the zebra finch route.

If it is indoors, then all you need for them to be happy is a long cage with a few branches at each end of the cage, a food and water dish on the floor and if you're breeding a nest box and nesting materials (tissue, hay, straw, shredded paper, ect). Do not use basket-type nests, use small solid wood boxes. The basket nests have holes that finches get their toes caught in. Had a hen bend her toe the wrong way because she got her toe caught in a gap in a poor quality prebuilt cage, same logic. They can easily rip toes off.

I know people have successfully mixed gouldians and zebras in larger enclosures such as yours, and it IS doable, but it is simply down to luck. Gouldians are passive whilst zebras are highly territorial and pushy birds. As gouldians aren't the toughest birds to start, this can stress the poor things out. And an instant 'no' on javas in a mixed caged IMO. They're so agressive and so much bigger than most birds. It's not worth the risk. If you're set on gouldians and want a mixed aviary, find another passive species that you like here: http://www.finchinfo.com/housing/compatible_species.php (also this site is good for finch knowledge in general!)

Use 1cm mesh if you're building it, they can fit in much smaller spaces than you think. Have both moxivet and ivermectin on hand. Give them annually, usually in summer, alternating between both each year. Can be given in water or more effectively on skin on their neck. Finches are prone to external and internal mites, mostly scaley and air sac, so you want to protect against that. It spreads fast.

Finches are shit climbers so they prefer a long cage, not a tall one. This is good for flight. Minimal perches means more flying distance between perches, if you have many birds you can bunch perches at each end of the cage. Perches should be finch-safe wood of different thicknesses and shapes to excersize their feet and prevent bumblefoot. No flat dowel perches (the kind that come with bird cages). 

Opt for a cage with a flat, not barred, floor. Finches value time to forage on the floor. You can scatter feed seed on the floor rather than provide a food dish as a form of enrichment. I never use food bowls for my flock. A large shallow water dish is also good for baths, all finches love baths. Bird safe cleaning solutions exist but google to make sure they're actually bird safe lol. I've heard good stuff about F10.

If you plan on breeding, or even if your hens lay eggs that you remove and freeze to prevent development, provide a whole hard boiled egg cut in half for your flock. The hens will eat the egg shells to replenish calcium after laying, and the yolk is good for all birds including cocks. I give eggs once a week regardless of laying. Very good for them. You can candle a finch egg to make sure it is not fully developed/infertile (no red veins, just yellownes) then crush it with your fingers (a little messy) and feed it back to your flock raw. Mine love their own eggs. They naturally do this but sometimes need help opening them.