Raising lawn level to 5 inches - many questions

Hello,
I finally decided to redesign my lawn. Walkway and the lawn are about 5 inches lower than my driveway, so I want to install border edging or sleeper between the lawn and the walkway, this way I will keep the walkway below the driveway and the lawn, and then raise the level of the lawn to the same level as driveway.

Now I have many things to decide:

1. Border edging or sleeper – if I use wooden ones, will they get rotten? I will, of course, use Cuprinol or similar product to protect it from rotting, but there will be a constant contact of the edging/sleeper with the ground, will I have to change edging/sleepers frequently, i.e. every 2-3 years?
2. At the moment, the lawn is still full of weeds and moss. The soil has high concentration of clay, or exhausted, therefore I am getting a lot of cracks. I am thinking to kill off the weeds first by covering the whole lawn with a black sheet (where could I buy one 5.5 m x 5.0m black sheet to cover my lawn?) for a couple of weeks, cut the grass as short as I can, then put about 1-2 inches of sharp sand, then 3-4 inches of top soil and finally roll turf on top. Will such method work and do I need turf fertilisers? If not, what should I do?
3. I was suggested to either make the lawn dipped at the centre, or in contrast higher at the centre in order look larger. Would you know which way it would make my lawn look larger?

Thank you.