Back in the 80's / 90's i had to get all of the Lionel 5700 series wood side reefers. I completed that task as the hunt was better than having them (which I still do).
I do have some McCoy and ETS trains, just get what I like as I do not need everything.
Got involved with prewar "O" and limit myself to the electrics 15 series/248/250 series and just stick to the 4 wheel cars. This way the cost is less as I buy junkers.
Also got involved with some standard gauge and jut keep to the electrics 8/33/38. On the cars I stick with the 100 series and the have some 10's series. The 110 series cars are reasonable as the others are out of my price range. Also have 35 and 36 passenger cars which are reasonable.
Just buy what you like and can afford and have fun.
