@Relevance Sure I'll try

I heard about this cool Challenge...

Depends upon what you are interested in: regular planes, helicopters, airships? Or cars, boats, ships, sailing boats etc.

For historical/ scale planes, honestly whatever I try to build, as soon as I started building, I found.ojt there are at least half a dozen instances of this plane for download already, most of them with far more detail than I can ever make.

However in my personal opinion, general sportsplanes, are vastly underrepresented, other than the ubiquitous Piper Cup. I could do with some more Piper, Beech and Cessna planes with a few Socata and Grob mixed in for good measure.

On battleships and tanks I don't really know because I don't really care, but on cars, there seems to be a lack of 'average' street cars like a Toyota or Volkswagen or even sportscars like a Ford Mustang.

And yes, there can always be more helicopters.

Build tanks and cool ground based stuff