The most important point is to have a clear understanding of what you want to
do in your yard.
What is the purpose of your yard? Is it to hold whole trains until they make their run - i.e to function like staging?
Is it to be a place for passing trains to exchange blocks (groups) of cars - i.e. drop of cars and pick up cars - say a small yard where two railroad exchange (interchange) cars?
Is it to an efficient sorting/routing point - where cars will be coming on trains from several directions, and be sorted into blocks going out in several directions - i.e. to be a classification yard?
Is it to be a local yard - essentially work space for a local crew sorting the cars in their train in preparation for taking the train out and serving local industries?
Is it a place to collect coal cars from several mines before putting together a train to take the cars down towards the coast, or where cars with different grades of iron ore are held until it is time to load an ore ship - a marshaling yard of some kind?
Is it a place where commuter trains are parked between the morning rush hour and the afternoon rush hour, or where passenger cars are taken to be cleaned and restocked before their next run - i.e a coach yard or something like that?
Is it a place where trains swap power, going from the plains into the mountains or the other way around, or where trains will stop for engine servicing - coal/fuel/water/sand - i.e. more of an engine terminal or helper base than a freight yard?
You mentioning 89 foot auto racks. Is your yard a car destination of some kind - a place where cars are actually loaded and unloaded, rather than a place where cars are just sorted or held for a while - like an intermodal (container) yard or a loading point for auto racks by a car factory, or a distribution point for cars - where cars are transferred from railroad cars to trucks?
There are many types of yards. Having a clue about what you want to model is a good idea.
Likewise, it is smart to have an idea about the mechanics - how many and how long trains will be coming into the yard per operating session? How many cars will be coming in before some cars go out?
How many destinations will you need to build blocks for at the same time? Will other trains be passing by the yard while you are sorting cars in the yard?
Can't recall if you explicit have stated what scale you are in, but I expect H0, based on your curve radii.
Here is e.g. a small 12 foot plan I drew up for a friend for a small end of the line terminal mainly for containers and auto racks:
Note how few auto racks will fit in 12 feet of space, in H0 scale, each 89' car is about one foot long.
If you need to be able to switch 6 auto racks from one track to another - i.e. pull them forward past a switch, throw the switch, and then push them into another track, you need 13 feet of length - six for the tracks holding the auto rack, one for the crossover between the tracks, and six for a lead.
Smile,
Stein