It is for a school project. I'm not familiar with weldment, I'll look into it. I went ahead and tried both GSD and Part Design but I don't know how to get the piping to stop at the next surface. I get an overlay, it wouldn't be a problem but I have weight restrictions and I don't know how to trim it back.If you want a solid model, use Part Design.
The only sculptured surface I see is the wings; so you might want to use GSD and then convert the surface(s) to a solid with Part Design. (But those wings look pretty simple, so you should be able to model them directly in Part Design)
I would model the components (engine, left wing, tail, wheel, etc) as a CATPart and then assemble all the parts into a CATProduct. The frame could be done as a single CATPart weldment, or a sub-assembly of individual tube parts.
Is this a school project, or just something to do for fun?
The Pipe Design or Structures workbenchs have special tools to easily handle the pipe ends and other things..... but it will take more steps and I know there has to be a faster way.