LOL,
With all respect Nathan,
Why do you think that there is no reply yet?
How much did you surf this site already for the tips you asked?
Those questions are part of the basics of diorama making, they have been covered a million times over all the modeling forums and in "How to " books, so you should at least show some goodwill of your part, show some work you did, research you did , something!
This forum is great, but it can not hold your hand for every step you want to make.
Start by buying Shep Paine's book about Diorama making and then start with a dio about 80 % smaller then the one you are planning.
Oh, download Scalecalc.exe (google it) , you can exactly calculate the difference between 1/72 and 1/76
Claude