Tackindy
It appears that you have 3 "mainlines",a blue line w/long spur, green line w/staging yard and the elevated gray line. First, just as info, are you controlling via DCS, TMCC or Conventional or a combination? I also appears that none of your mains are interconnected via crossovers.
Are you anticipating having each of the mains, plus adjoining spur or staging tracks, as a separate power district[3 total] with of course its own transformer or separate throttle power supply? What load of engine motors and lights do you plan for each district? You can toggle selected staging tracks and or the spur for disconnect which when not in use will isolate cabooses and parked engines.
You have 75 and 100 watt transformers so whether they will suffice depends on the train load of motors and lights they supply in their respective districts. You have led-ed passenger cars which is a big plus. If you have engines with modern motors that is also a plus load wise. Consider that even a modern engine with a single motor can pull 25-35 watts depending on consist load and speed. So the answer to your transformer question is to assess the makeup of the equipment that you will be running in each district and its estimated electrical load.
For example, if you were running an AA combination of 1993 Weaver E8s with four motors, forget the small transformers. I used to run that combination with 5 incandescent lighted passenger cars in tow and it is a big load wattage-wise. I note this to indicate the difference in modern and older engines.
As long as you have secure track connections and have ample railpower feeders to avoid voltage drop, the length of track will have only minimum affect on the electrical demand--its all about the train load.