Advice of modelling a plot of land for my residential area

Hi there all Blender-gurus. Here is a probably crazy query from a Blender lover that is in the beginning of my Blender career.

I have began to make a 3-D model of the area I live in. It is a place with 9 houses - 4 appartments i each building and some small complement-houses for trash and more.

The query is about when I make the plot.
I have done it with vertex and made it from a drawing and also been out measure some part.

The plot is mainly of three types.
1 Concrete plates
2 Green areas in this version this will be Grass in
3 Asphalt
I have not began with materials yet and is still ongoing with the geometry and it is still totally flat.

On the attached png I have three marked areas - frames. This is areas that will be green areas.

My first question is - Is it totally crazy to have this Muli - ngons when I will lager add materials on this areas. Should I divide them into smaller pieces? But it is in real those areas that is connected in real life.

My Second question is - when I am ready - I want to add some small height differences. To get some thickness - is it recommendable to use Solidify Modifier and apply it and then begin to work in the Z axis.

I would be so happy to get some advice in this project (Just Hobby-project)

Have a Great Day all
// Erland

Try Archimesh Addon (default Addon)

The full lecture in the video below will be helpful.