As a newcomer to the hobby, I was originally planning to build my layout and collection with only Lionel products. Run it all with Legacy and keep things simple. However, as I get further exposure to the hobby through the forum, the OGR Magazine, YouTube, etc, I see that there's a lot to be had outside of just one brand. Gargraves track and Menard's buildings are great examples. These don't directly impact how I run my layout and can add tremendously to it.
But what about locomotives and rolling stock? Are scale items fairly consistent across manufactuers? Let's say I have two boxcars, one from Lionel and the other from MTH, or Atlas, etc, will they work well together, or do they clash? (eg one could be slightly longer or taller than the other and thus look bad if running next to each other).
Specifically in regard to locos, I know the question of control systems comes up, which was my main motivation for sticking exclusively with Lionel and LC+2.0/Legacy. But here-and-there I will come across a loco that I haven't found from Lionel, or Lionel has made it, but another brand I'm looking at has the same loco at a better price. I'm sure it's doable, but is it practical? Is an ERR conversion easier or preferable? Am I better off waiting for Lionel to make the same loco? With the closing of MTH, I've sometimes wondered what I would do if Lionel were to one day bite the dust, so the idea of "diversifying" my layout has come up a few times.
Thanks for your thoughts.