You’ll get a much more cohesive look if you complete your design first, and then purchase your structures as opposed to vice versa.
When starting a design for a customer, it’s fairly common to hear something along the lines of, “Oh, by the way, over the years I’ve been accumulating a number of structure kits and would like as many as possible incorporated into the design”. I can understand their point of view. They’ve spent a fair amount of money acquiring them and, on individual basis, each kit is interesting when viewed in isolation. Unfortunately, I usually have to be the bearer of bad news and tell them that having randomly acquired structures drive a design is not in their best interest. Often the kits were purchased long before any theme for the layout was established and, as a consequence, are generally unrelated to each other in any way or to any theme we could come up with. One or two may fit together but certainly not the dozen or so we are usually talking about. The other major problem is that structure footprints take up a lot of space and forcing a design around these very arbitrary placeholders is a case of putting the cart before the horse.
The best approach is to hold off buying any structures until after the design is complete. Establish a theme and goal for the layout, create the design, and then select your building kits. Let the design drive structure selection, not vice versa. The end result will be groupings of structures that fit together plausibly and a track arrangement that flows much more seamlessly. What about all of those kits? There’s a company called ebay that can help you with that! If that’s not your thing, then give them away. I know it’s painful but sometimes you need to admit that you jumped the gun, need to bite the bullet, absorb your losses and start over the right way. Look at the bright side, you get to go structure shopping again!