Your project is pretty descriptive, however a creative brief will be necessary.
We can provide you with a concept idea in a wireframe format, but everything really depends on what your coder is capable of in terms of implementing and what your expectations are. Do you want your app to be as good looking as Vine or Instagram, or do you want it to be plain and just backgrounds -- If your developer can't code in the proper graphics and hover effects, etc -- we need to know what we are limited to.
If you go cheap, you get cheap. There is a psychology to branding and design that most people on here do not appreciate or understand.
Do you have a logo? If so is this going to be an extra bid? If you are having a designer work on the app itself, the logo needs to match the design or else your entire identity will suffer and people will not use the app.
The visual appearance of an application is what makes or breaks it, generally.
This is what I gathered from your list of requirements:
Designs: 4-8
Why 4-8 designs?
Splash Screen (loading)
Login with Facebook
Friends List (Top 3, Top 5, Top 10, Top 15)
Pop-Ups for the actions (Share, Rank/Rate, Purchase, Thank You, etc.)
These will ensure that your developer codes things in properly, you will receive a style guide as well for your developer to follow to ensure the successful implementation of the graphics so he does not "stray" from the designated work.