1. The best/easiest ... is a matter of hot contention...
I am (to no one's surprise) a fan of FSDS (commercial product, sold by Abacus PUblishing in the US, and through other distributors in the UK and Europe). It is a dedicated flightsim modelling program that can create a true FS-X model, and with certain add-on utilities *FSDSxTweak* and some manual editing of text files, can also add the 'eye-candy' that is now de rigeur in FS-X models.
gmax, however, is the more powerful modelling program and up to now has been supported by the Microsoft/ACES team with specific modelling tools to create the FS-X model. Also, it is free (it comes in the FS-X Deluxe version dvd)
Caveat: To use the FS-X SDK, you need to have bought the FS-X DELUXE version....
I speak Spanish, and Standard American English (somewhat adulterated by years of working with Scots, Geordies, a motley collection of Englishmen, and with good ol' folks from the American South). LAtely, though, I catch myself saying words in Hinglish, Venezuelan SPanish, ... Mon dieu! Je ne knows pas anymore what I spreche!