Ok, now that I got the basics out of the way, we can go onto the more advanced 1/32 studies...
So if you are interested in collecting the more "toy grade" stuff, as in not plastic models you have to assemble, you're pretty much going to have to live with mostly FOV and 21st Century. There are exceptions however. Some companies like Airfix and Britains made some plastic and metal pieces that will go with the 21st and FOV pieces size-wise, but they aren;t quite on-par with them. For one they are generally unpainted plastic, or really blandly painted metal. They are also old, so you'll have a hard time finding them, and then once you find them you'll need to repaint them if you want to display them with the good stuff. They might have moving wheels (Like Britains 1/32 Daimler scout car), but moving tracks on this old stuff is rare (like the Airfix sdkfz 251 and cromwell). There are other manufacturers that some might mention, like CTS, but in my experience these items are too small to fit in.
Now if you are open minded to the non "toy grade" stuff, you'll have a few more options in terms of plastic model kits. Several companies produced 1/32 scale model kits back in the 70s and 80s, and they are quite unique offerings that oftentimes are vehicles not covered by any 21st or FOV productions. These companies include (but are not limited to) Monogram, Airfix, Renwal, Lindberg, and Italeri, and Bandai. The Airfix and Monogram kits are where you will find the most variety offered, and they are also the most common. Airifx offers 1/32 versions of the Crusader, sdkfz 250, humber car,M3 Grant/Lee, and 17 pdr AT gun. Monogram offers an sdkfz 232, jagdpanzer IV, brumbar, M8 Greyhound, M20 scout car, Flakpanzer IV Ostwind and Wirbelwind, M4 and M4A1. Renwal had a M41, a Duster, an Ontos, a SP howitzer, a nike missile set, and a huge atomic annie kit. Linberg had a sdkfz 222, a higgins boat, a PT 109 and M46 (I think). Italeri makes a few guns, like the Russian ZIS 3 and German PAK 40. Finally there is Bandai, which is kind of a tricky one. They made a "1/32" scale sdkfz 234/2 Puma that was actually more like 1/30 scale, but they made a few 1/30 scale vehicles based on the panzer IV that are actually near 1/32. Those are the Hummel, Heurshreke (sp?), and the jagdpanzer IV. There also a few poorly scaled 1/35 kits that can be counted as well. Those I've come across thus far are the vintage motorized 1/35 Tamiya M10, M36, and M4A3E2.
Figures are in abundance in this scale. Most are not painted, but that shouldn't be surprised to anyone who's seen bags of green army men. There are some pre-painted figs out there that work with 21st and FOV, namely Oryon 1/35 scale stuff, Dragon Can-Do 1/35 scale stuff, and some figarti stuff, but generally you have to pay more for them. If you want cheap figs just go with the airfix or italeri figures or the many repo companies out there.
1/32 civilian vehicles are also easy to find. There is a plethora of stuff in the 1/32 market that would be suitable for civilian vehicles for various theaters. Most lacking are probably the stuff you might see in Europe during WWII, but even those can be found with enough diligence (hint: vintage matchbox and Japanese companies).
Diorama stuff is also fairly easy to obtain. If we're talking the basics, just go to your local Michaels or Hobby Lobby during a holiday and go check out their diorama section. Not all is usable obviously, but you might come across a cobblestone road mat or field of grass. Other more war-centric stuff is available from several companies. The one that stands out the most is Build-a-Rama. Tons of great stuff, but it can get pricey. Also companies like figarti, frontline and other make diorama stuff.
Well, that is a lot of info, and I'm sure I'm missing a lot still, but I am trying not to overwhelm you too much lol
If you ever have any questions, feel free to send me a PM.
-Kevin