I have recently been getting into developing mods and games, I have been working on a Minecraft mod like the game I am now planning to design. I was wondering on a few things:

1) Is Unity 3D good enough to support a massively online RPG?

2)If using Unity 3D does it HAVE to have a single player mode? or can It just be a multiplayer game?

3)If unity cant support a MMORPG and hopefully but not required a single player mode can anyone recommend a game engine that can?

Please answer ASAP

One more question.

If it can support a MMO would I have to get the server set up before building the world? Or could I leave it until the world and guns/cars/features are all built and added in

Note that "MMO" has a meaning, and an individual cannot afford it. The term was originally used to mean worlds with more than 100,000 concurrent users. For any such game the biggest problems are not the game client, but instead the server architecture and the content. "MMO" architecture costs many hundred million dollars.

Unity has networking support.

Your game written in Unity could be written to rely on network data to run the game and coordinate the world.

Building networked games in Unity can get very tricky. Many features of the engine were designed for local use only. Many of the fancy simulator tricks done for advanced online games cannot be easily done in Unity. For example, running one simulator in the 'future', or rewinding the simulation to insert an event back in time, are not built in.

Many people have built simple network games with Unity. Some people have built online persistent worlds with Unity as the client; in addition to writing the game and a lot of network support code they also need to write the servers.

1) Can Unity be used for online games: Yes of course, many online games were built in Unity.

2) Can Unity be used for an MMO: depends on your definition, but AFAIK there are also games with persistent worlds built with Unity.

3) Does Unity have to have a one player mode: No, of course not. Unity is a pretty open multipurpose engine, there is little you cannot do, some things are just less easy to do than others.

But:

1) Does Unity do Networking out of the box: No, not really. You get some networking functionality, but if you really want scalable networking, you need to add a lot or use 3rd party implementations.

2) Is Unity an MMO engine out of the box: almost no engine out there is "an MMO engine" out of the box (I'm getting to that further below). Unity is not much different. Use for you client whatever you want, the server part often needs a very custom solution.

3) Is it a good idea to even talk about creating MMO's when you got into game dev "recently": No, totally not. Chances are good you have little grasp on the technical complexity involved with persistent worlds, and you try to run before you can walk. Also, MMO's are usually consuming 10+ million $ in cash just to develop, not talking about servers and maintenance to keep it running now. You really have enough money lying around for that?

About the MMO Engines: I know of 2 that where built for exactly that purpose...

- Bigworld: You could license the engine until like 3 years ago, then it was bought by Wargaming and is now proprietary for their own MMO games.

- Hero Engine: http://www.heroengine.com/ ... a lot of bells and whistles for MMO development. How good and scalable it is after the marketing blurb, I don't know.

Quick word of advice: either keep it to modding existing MMO's, or drop the MMO idea for good (until you get filthy rich), and save the multiplayer for later. Start more modest with singleplayer games, very simple one at first, until you get a better idea just how much work and money is involved in game dev. Try to finish multiple projects, each a little bit more complex than the last.

Then, when you feel confident you can build a game, try your hand at a multiplayer one.

Please answer ASAP

This makes you sound like a raging d-bag.

<sarcasm> My thoughts were: writing an MMO takes a big team years.... and you care if people answer some hours earlier? </sarcasm>

The more serious, less sarcastic comment: Its pretty pointless to put that at the end of your opening post. If somebody read that far and knows an answer he will most probably answer ASAP anyway.

If he/she happens to not open the thread when checking gamedev in the morning, and only does so before powering down his/her machine in the evening... your "ASAP line" he/she was not able to read will not change that.

This is even less useful as bumping your own threads, and might just look rude to people.

<sarcasm> Patience, my friend... </sarcasm>

Okay, I am leaving before I start doing the Yoda thing.... ;)

Considering how vague and generic your questions are I'm gonna go ahead and sum up what quite a few people are trying to get across to you:

You aren't ready to make the kind of project you're asking about.

Will you ever be? Possibly. I would say you should set your sights a little lower and decide on a more realistic goal. Unity can definitely make many other kinds of games if thats what you're interested in doing.

Since others have already covered part of it, I'll take a different approach and assume you asked the wrong questions.

I have recently been getting into developing mods and games

Fantastic!

Have you managed to complete a full single-player RPG? Making an online RPG is more complex than making a single-player one.

1) Is Unity 3D good enough to support a massively online RPG?

Do you actually mean a massively multiplayer online RPG? One with over 100,000 players at the same time online at once? That is to say, one million active subscribers?

Or do you mean just an ORPG (online RPG), like Minecraft is? Minecraft servers support like 30-ish players at once on one server, not 100,000 at once on one server. These are dramatically different scopes. When you start to reach a certain number of players interacting with each other in the same world, then it exponentially increases the complexity of the coding.

How many players, in a single server, is your game design requiring to support at once? Less than 50? Less than 500? Less than 5,000? Less than 50,000? Less than 500,000?

Each step up is significantly more difficult.

2)If using Unity 3D does it HAVE to have a single player mode? or can It just be a multiplayer game?

You can just have a multiplayer game in Unity. You aren't obligated or forced to have a single-player portion.