Not being able to do animations will be a serious limitation, but another freebie 3d modeling program is always welcome,
especially with the demise of support and development for gmax. When you have finished your modeling and have saved to the
3ds format, make sure you go to Vinka's site (
http://users.swing.be/vinka/ ) and get his 3ds to msh converter. While there
you will also find his spacecraft2.dll for quickly adding functionality to your ship (a very good method if your programming
skills are not strong enough to do your own ship dll files).
Animation for exhaust flames is hardly necessary, except maybe for the new Titans.
Another 3d modeling program you might want to take a look at is Blender. Learning curve is a little steeper for this one as
it handles things in a much different fashion than most modeling programs, but it has good tools and can handle the animation
that you might want to experiment with.
For doing textures and skinning models, I highly recommend going with The GIMP (of course, a freebie) as it has great
functionality as well as handling PSD support for layering (support missing in such drawing programs as Paint.NET).
Just a small reminder, if you are looking for resources for Orbiter, there is no better site than simcosmos
http://simcosmos.planetaclix.pt/ .