as a young person who really wants to delve into O gauge, I'm disappointed in what I've found...
At 33, I'm a baby as far as this adult hobby is concerned
Welcome to the O gauge under 50 club.
Some of the best model railroaders out there in any scale today are guys in their 30s and 40s modeling in O. Check out the work of Rich Battista, Norm Charbonneau, CSX Al and Dave Hikel. They have all posted plenty of photos to this forum as well as elsewhere on the web.
What is out there and what you have found so far may be different things. You seem to know about the MTH 20-20055 F7s. The MTH product locator feature shows a dealer with the -1 version in stock. Have you clicked on the "Find it locally" tab and called the retailer?
http://www.mthtrains.com/20-20055-1
the period that really excites me are the nostalgic years I connect with - those 10 years right before I was born
OK, so you are interested in modeling the Santa Fe in the 1970s. You have GP9s, GP30s, GP35s, GP38s, U25Bs, SD40s, SD45s and more to chose from. MTH lists 7 pages of premier line diesels, many in paint schemes from the 1970s. Add the MTH Railking Scale, Lionel Standard O and Atlas Master Line and Trainman diesels and you have plenty to chose from.
I can't have F7 switchers when they have to be tethered
So you want to run F7A units separately? You can already to that with the lead unit. If you want to run the trailing A unit on its own you can carefully remove the slave board and install a Proto2 or Proto3 kit.
I will say that Lionel's recent scale offerings - the '89 auto rack and '86 boxcars are going in the right direction. That's just the kind of item that interests me.
Great! Add in the Lionel and Atlas 60 foot box cars, the PacCar mechanical reefers from Lionel and Weaver, plus covered hoppers, 40 and 50 foot boxcars, flat cars, gondolas, etc. from all the manufacturers and I bet you can find more than enough era appropriate models to jam any freight yard.
We have more than 200 different plastic, aluminum and diecast freight car models available to us today in O scale. Many fit in on a 70s era layout. To get a better handle on what is out there you might want to check out the O Scale Freight Car Guide series.
https://ogrforum.com/t...le-freight-car-guide