I'm planning to make livable area in the basement(55 sq. m)  which could initially be leased and used for personal use later.Current height of the basement is about 205cm.
I'm planning to build a living area in the basement which could initially be rented out and may be used for personal use later on.  Current height of the basement is about 205cm. I am thinking to have somewhere close to 230cm finished height which means they need to dig around 255cm to make a room for new sub-floor. 

What is the best practice to do this i.e. how many layers of insulation is sufficient ?

Walls are not deep enough i.e. not more than 10-15cm from current floor. Is it a normal practice to

Should I also put in new drenering from outside ? Some contractors said it's enough to do drenairin

Please suggest

Thanks