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Orandas can grow up to 8 - 12 inch. For the tanksize is rule of thumb minimum 10 gallons per fish, better more, or 2 litres per inch fish.

With the tank you will need - or better I recommend to have - a good filter, pump, airstone, peasized round gravel, live plants, AQ light, gravel siphon, nice centre piece ( please avoid sharp edges and small holes as the fish can get stuck...)

For the water I recommend conditioner to remove chlorine and chloramine from tap water, also beneficial bacteria to speed up the cycle and test kit for Ammonia, Nitrite, Nitrate and pH   ( like API Master Test Kit for freshwater fish )

Before adding fish you should set up the tank and let it cycle. I don't know if you are familiar with the Nitrogen Cycle. If you aren't let me know.

Basically if you are looking for healthy fish, take your time and visit all pet shops you can in your area. Look out for how clean the tanks are, how the fish are kept, are they wiggling at you when you look at them. Are the fins nice and not ripped, no spots or blotches on them like white and fuzzy or slimy things.
Are there tanks in quarantine, are dead or lethargig fish in there. Does the store smell clean... all those different things to look for...
AND very important. How knoledgeable is the staff.

A tricky question or suggestion you can test their knowledge: To go in there, telling you just filled your tank with water and you want to buy 1 neon tetra, 2 goldfish and 1 silver dollar.
If the staff grabs the fish net you know that person doesn't know anything or is only interested in making money but doesn't care if the customer will be unhappy facing trouble in the AQ and aslo doesn't care for fishes welfare. Why?

Neon Tetras are shoaling fish they should be kept min 6-8, better more. They also need different water conditions than goldfish.
The Silver Dollars are quite bossy and agressive, as they belong to the Piranjas.
So this combination of fish is not compatible at all and a knowledgeable staff immediately would explain that this cannot be sold to you, also that the tank should cycle first

I know you'd cover that Hanna. I'd go bigger but it also should just be ok. It's better to have about 40L per goldfish and I believe Oranda's can grow quite big. So the bigger the better

Correct me if I'm wrong, but technically - theoretically having 2 orandas in a 48L tank is still okay, but not ideal? Not that I'm planning on getting a 48L tank.

well, in this case go for a bigger one.
48 l is sort of ok, but not ideal. Also smaller tanks mean more work, bigger tanks mean plenty of room for the fishies to swim, thrive and be happy and much easier maintenance for you, so you can enjoy your fishes much better

Any particular brands you would recommend? I'm going to have to save up for it, and I'm a teenager so I don't have thAAT much moneoy.

Tanks.

Would you recommend putting any live plants in the tank? If so, what kind of plants?

Oh yes, live plants are very good.
I only have a couple of artificial ones in the 150 l, just for a little colour, the rest is live ones: Hornworth, Ambulia, Elodea, Java Fern, Valisneria.

I don't recommend snails, they multiply tooooo quick.
But goldfish are grazers too and with not too much light algae in a goldfish tank shouldn't be a too big problem.

BTW, I answered your question in your messages 

Have a GOOD NITE 

UUUPS, sorry for that... I think I never get it right with cm and inches, LOL, I apologize for that

Novaguin: Nossie is right.

I've never heard of them but I just looked them up and they look good with the filter, media and heater included. Which one are you looking to get?

Hanna: I have tried to do big water changes but it is normally back at 40ppm Guess it's alright cause that is still a safe level However I'm not stressing to much because Sunshine's moving out of that tank soon. Oh and I've already brought stresszyme, bummerrrrrr! Should be fine though.

Well, the only place I've been to is Pet City. On their website, they have a  Juwel Starter tank which is 56L for $139. I realise it is definitely not big enough, but Juwel does seem a lot cheaper than AquaOnes.

I'm always a bit iffie when buying stuff on ebay. Main problem is I see the tank getting crushed, or the seller not being reliable. What should I type in? Most tanks that show up are in the $300+ range.

Did you read the message I send to you last night?

This is a very good price,  , compared to what our 34l did cost; $180.
What does it include?

There should also hopefully be ones in your area which you could pick up instead of getting them sent to you, which would save you alot of money. Ebay is incredibly reliable in my experience, that is why it does such good business so I don't think there is an issue there. Just make sure you check out their feedback rating.

The Juwel tank includes: Tank, Light Unit 60cm, 1x15w Light Tube, Filter. The tropical one has a 50 watt heater for an extra $10. Doesn't specify what filter though.