"""""""""""""""MoI obviously doesnt have all the tools for extremely high-precision surfaces as Autodesk Autostudio might have, but so far I feel like it has enough precision for me."""""""""""""

MoI's precision and surfaces will be just as high quality.... Surface at G2 and curve generation at G3... Nothing wrong with that...........

""""""""""""1. Is MoI capable of creating complex parts and form-transitions as airplanes and cars have? """"""""""

For what you have described, Yes.... MoI can draw precision NURBS curves and surfaces as you are looking for.

"""""""""""""Or to put it differently: Is there anything MoI would struggle with especially?""""""""""""""

but you are talking about going out of "sketch"... Tracing out of blueprints and such will have you need tools for surface matching and such that MoI doesn't have.... You would struggle here.. Even run into areas that cant be handled by the current toolset.

The grouping tools are up to you...