Hi, sorry for the delay. As I understand it, you want to make a business out of it.
When it comes down to developing for "the real world" there are various considerations to make... will you need a salary for working at this? do you have an initial budget? etc.. I'll try to not go into this kind of stuffs, but please be aware you will need to MEAN business if you're going into it.
Here are some random thoughts about this:
With a startup with limited resources, it really depends on what you can buy and your developing skills; it's a matter of how many different tasks you can carry out and how fast.
For example, will you create your own game objects and maps yourself (please note that rigging and animating often are part of this task) or will you need to hire a 3d designer? Or you will rely on the vast collection of assets in the various stores? (take a look at this)
Same goes for developing game physics, network infrastructure,game paths, game levels, world generators, menus, AI... you can find something already built in the various stores...
A 200$ game pack can save you weeks of work if you are weak in a certain area..
But before all this, you need to know your own skills to understand if you're able to complete a task, how much time it requires you and based on that so decide what to buy and what to build and ascertain if you'll be able to use an asset and integrate it with others.
If your friend really hasn't ever done anything in Unity (and other software needed as 3D modelling software), that's the worst situation, please look at some tutorial, read some best practices, and build something... a test project, maybe also a first part of this very project, before thinking to start seriously.
Note that there are 100s of ways to accomplish a task, but there are few that are optimal, you'll need a game that would be playable on the highest number of device possible, and so you'll need to write efficient and optimized code and use adeguate assets (you'll also need to be able to understand if an asset you're buying is of good quality and suited for your goal), but also being able to write maintainable code, so that you could easily to add on top or expand the current code base and not being forced to rebuild it for a new feature or else.. If you're new, I would suggest to pick a developing style/model and life cycle that would let you test and optimize along the way.
Another thing is certainly organization and I would strongly suggest to use a project/task manager/planner software and obviously implementing a version control system like GIT is quite a requirement for a serious commercial business.
A complete knowledge of the extent of the project is most certainly necessary, so I would suggest sitting down and think very hard at what exactly you want to do.. examples: