Hiya

This is my first post and am after some advice about how to lay a new lawn. I have inherited a garden with my house which is all uneven, not well kept and frankly looks shocking; the grass texture is also straw-like.

I want to essentially have a flat lawn and know what I have to do but I have some questions:

Before rotavating the soil and turning it, do I need to dig out the existing grass and throw it away? Or just rotavate over it?
Do I need to take into account any bordering? i.e. should the edges of the garden be set lower?
I'm going to be using seeds - how long will these take to grow into a full lawn and are there any special considerations I should make?

Thanks