Road trip to Panama from California. help me if you have done it!

Hi everyone, i am back to this glorious site, looking for help to prepare my newest adventure. I have a subaru Legacy 1999 station wagon, i recently tuned it up and changed the engine to work on vegetable oil. Now i want to use it in a road trip trough central america, from California to Panama. i want your honest and most accurate response and information about this topic. The following are my main questions.
1. whats the best way to go across Mexico in the quickest possible way. I have been there many times and dont think i wanna spent much time there?.
2. what would be the best route to take from Chichen Itza to Guatemala and from there to the other neighbouring countries.?
3. what places should i visit in each country, taking into account that i wanna spend nomore than 10 days in every one of these nations.?
4. what do i need in terms of dealing with customs and border crossings in all of these countries?
5. what about my car, what kind of papers do i need to take with me through the trip?

At this moment, these are the main questions coming to my mind, i beg you guys to Please help me out with this beautiful dream of mine.

sincerely

Green Resistance.