How do you get one item to Masterwork?
Are Masterwork items the only ones that can get to +12?

Thanks in advance

You have to ID and reroll items using Master Enigmatic Scrolls and it has a chance to make them Masterwork.

Yes.

Wouldn't getting a +12 item be incredibly difficult? As you will need many +11 +10 items?

Most likely because its RNG based and you'll need to spend a lot of tier w/e fodder (has to match what you are enchanting) to enchant with.

Correct me if I'm wrong

Does that mean in order to get a +12 masterwork item you would need AT LEAST 3 other masterwork items being +9, +10 and +11, or possibly more, in order to get your desired item to +12
That also means that you could be spending several thousands of gold in order do that right?

yes and no, you would still be spending thousands possibly 10-20k on a masterwork.

but you do not need to masterwork fodder to up a masterwork.

How do you get Masterwork scrolls?

lvl 58+ dungeon drops, (from last boss) or buy with battleground credit or buy with nexus credit, alors drop in Nexus Traverse

Can you buy from players?

yes, average is 150g (on mount tyranna)