Model train questions?

HO scale is really too small and not robust enough for permanent outdoor use. N-gauge is even smaller and totally unsuitable.

G scale is designed to be large enough to survive outdoors, it's often referred to as Garden scale for that reason but the G comes from the German word for "big": "grossen" .

Although G gauge is universal, G scale isn't. Bachmann use 1:20.3 scale for their "Spectrum" range, and 1:22.5 for their "Big Haulers". Other manufacturers vary from 1:20.3 to 1:32 scale, but 1:32 scale is identical to 1 gauge which uses the same track gauge as G.

You can run mixed scales on G gauge track but there are limitations; anything from 1:20 to about 1:24 won't really be noticeably very different upon casual inspection, but a 1:32 scale model definitely looks too small next to 1:24 or larger scales. You also have to make sure that all track clearances are constructed to suit the largest scale you plan to run.

Larger scale models cost more but are more robust and increasingly resistant to adverse weather. They are also easier to model realistically. Smaller scales are cheaper, more compact and so easier to store, but as the scales get smaller they become less robust and increasingly toy-like in appearance and movement.

I cannot comment specifically on Bachmann as I have no experience of it, but there are plenty of railway modelling forums and websites where you can get a feel for the advantages and disadvantages of each brand. Märklin are excellent, and have very good resale values, but you do need deep pockets to begin with for their products. Others will be significantly cheaper (though never truly "cheap") but may need more fettling to make them realistic and reliable although for some that's a big attraction. You'll find that some modellers just like to buy, install and run, others are all about building and constructing and let others run their creations. Others just like building the track layouts and scenery.