All of what you ask for is doable.
To populate the sections based on the dropdown value selected will require scripting. All of the individual script commands are documented but putting then together into the combination that you need is not. This particular topic has been discussed and samples have been built multiple times on this forum. I would start with a search on this forum.
There are also numerous books written as well as samples provided in the product that can show you the concepts involved with scripting but no one can anticipate exactly what you are doing so you will not find an exact sample that does what you want.
The ability to show/hide different sections of the form has also been discussed and samples written for it on the forum as well.
I suggest that you dive in a give it a try and if you get stuck ask more specific questions on this forum and any of the people who watch the forum regularly will help out.
Paul