I still recommend three power districts as described in my reply above. Each PD would be a separate power supply or transformer handle. Blocks within the PD's are up to you. Were it my layout I would make each passenger station track a separate block, the feeder track from the mainline to the stub end freight yard a block and each of the stub end sidings a block. There appears to be a long interchange track between the inner and outer loops, make that a block. If you have any parallel passing tracks on the loops make them separate blocks, I only see one. I am using the term "block" to indicate an on-off switchable segment. The other segments of track can be powered from the PD source without an on-off switch.
Make sure you have a block to park your FlyerChief engines when you are not using them. They get really annoying sitting on a powered track beeping while waiting to pair up with their controller. Similar with your conventional engines while you are running FlyerChief or Legacy, you need a dead track for them.
I would use the Legacy controller to run the Conventional engines as well as the Legacy engines. That gives you walk around control and you will not need access to the transformers so they can be mounted out of sight if desired.
Do not rely on the Gilbert 2-Train switch for a permanent layout, put in insulated track joints. Fiber pins work for Gilbert track, MTH makes insulated rail joiners for the SHS/MTH sectional track. Since your have no reverse loops and your track plan is not "complex" the layout should work fine with the Legacy signal on just one rail so no need to install the small coupling capacitors. You can then also just put the gaps in one rail for the PD's and blocks rather than both rails.
I do not see any uncouplers in the track, I think in the long term you will want them. Best to put them in now. from a quick scan of your pictures I see 12 places I would put an uncoupler. You also need operating car track sections for some of the accessories. Any plans for trackside controllers such as semaphores or signal bridges? Will you want them to auto stop the trains or just indicate status?
How do you plan to control the layout, conventional controllers or LCS? If conventional controls where do you plan to locate them?