Building system - economic strategy, RTS

Hi guys,
I plan to create a strategic game in which the player will build his own city / village. I am at the stage of game design and tool selection. I chose the unity engine.
I have a few questions:

1. What do you think about generating terrain? Use standard tools from unity or some other way?
2. I would like to be able to mark the area in a similar way. The grid would be drawn over the screen regardless of its shape. A similar editor can be found in "Banished". How to do it? What tools, resources to use?

If you have an idea how to do it or you have already done something like that, I am asking for directions.