Maya's default unit should correspond to Unity's default meter units. If you make something 2 units tall it should import nicely to be 2m in Unity. Very handy.
As for what to set your grid to, (Display > Grid > [ ]) that's up to you, and it depends on what you're working on. You have 3 basic options:
Length and Width - Sets how large your grid is in the scene. If it's 10x10 and you're working on a whole village, you'll probably want a larger grid.
Grid Lines Every... - Sets how often lines should be drawn. You can have a grid line drawn every 2 or 3 units if you wish. Note you can have this be less than 1, which will draw multiple grid lines per unit, although this may be better handled with..
Subdivisions - How many lines you want dividing every grid line. I have this set to 10 currently, which means each subdivision is 1/10th of a unit. You may want more or less depending on if you're working small or large.
Play with these settings. Make sure you can keep track of how much a unit is, coloring grid lines and subdivision lines separately helps this. Find something that makes your job easier when you turn on grid snapping. I'm new to Maya, so it kind of took me by surprise how arbitrary the grid system is, but I like being able to set up whatever lines and subdivisions I like and have objects neatly snap to that.
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As for what to set your grid to, (Display > Grid > [ ]) that's up to you, and it depends on what you're working on. You have 3 basic options:
Length and Width - Sets how large your grid is in the scene. If it's 10x10 and you're working on a whole village, you'll probably want a larger grid.
Grid Lines Every... - Sets how often lines should be drawn. You can have a grid line drawn every 2 or 3 units if you wish. Note you can have this be less than 1, which will draw multiple grid lines per unit, although this may be better handled with..
Subdivisions - How many lines you want dividing every grid line. I have this set to 10 currently, which means each subdivision is 1/10th of a unit. You may want more or less depending on if you're working small or large.
Play with these settings. Make sure you can keep track of how much a unit is, coloring grid lines and subdivision lines separately helps this. Find something that makes your job easier when you turn on grid snapping. I'm new to Maya, so it kind of took me by surprise how arbitrary the grid system is, but I like being able to set up whatever lines and subdivisions I like and have objects neatly snap to that.