Learning it ?  Not long at all... 

Mastering it ?  Never happen... 

Your first aircraft, start to finish; textured, animated and ready to share ?   300 hours   

IT's okay - I"ve been working at gmax since .... 2002 ....

Well, it will definitely create a challenge for you, if you have no experience in 3d modeling. Well the motivation will keep you going to create something unique. Expect the skill to come with time and know how to come quick. I started, I believe using Gmax oh around 2004 and or so, about 2 1/2 years and I can create great model with a little patience. I would look up as much tutorials and help, also install the game pack and remember to make backup's of your projects. -Good luck!

Setting up 3-views (top bottom side) is the best way. You can use bitmaps as backgrounds, but you'll find out how troublesome that can be.

Keep studying tutorials and the help files. Learning how to use three boxes as "screens" texured with the views is the best way to do it.

What airplane do you intend to model first ?

Any plane is fine. You can decide as you go, what level of detail you're willing to strive for. A highly accurate Warrior can be just as difficult to model as an A380. The trick though, is to have a passion for the plane, because by the time you're done with it, you'll feel like you're married to it 

The P38 tutorial is good for getting a feel for it.. there are dozens of others. The process is literally so multi-sided, I'd say that actual modeling is less than half. Animating is a handful, and the oh-so-important texturing is a vocation in itself...  THEN you have get the geometry and physics and contact points figured out... Dynamic virtual cockpits are a test, too. Oh.. and don't forget the panel(s)   

(if you have a wedding planned for the near future, you might wanna choose between your new bride and aircraft modeling      )

All of the above is really good advice...it all sounds very familiar! One other thing to consider might be to tackle the learning process in bits, instead of all in one go. Developing your first complete model may take quite awhile longer than anticipated (mine took half a year, followed by several more months of ongoing "tweaking"). For example, if the P-47 is your style, check out an existant model that you can redesign your own textures for. You could also try adding your own effects or modifying a 2-D cockpit (a 3-D one requires having the model's source file at hand). Focusing upon one aspect of modelling at a time will be more manageable; you will then be armed with the knowledge to be able to tackle it without problem, once work on your first big project is underway.

nice p51! lovely