I have a tank 4ft x 2ft x 14ins high

I am going to redo it again but this time it will have a 1/4 ins inserted glass top.

My questions are:-

How deep a good potting soil?

Can I use a mix of Spag moss on the bottom and a top of potting mix if so how deep of each?

How many plants can I use? Is it better to have a large mix or a small mix using the same plants in either groups or scatered around?

A ground cover type of plant between gaps?

Driftwood and rocks?

What would be the best plants to buy "Australia".

Any other useful info would be appreciated

Cost is not my biggest concern