I apologies for the delay in reply.
The KISAE DMT-1250 does not monitor the battery, other than voltage and current that is being supplied from the DMT1250. That leaves a lot of holes, while many use voltage readings to determine State of Charge it can be fraught with error. A battery monitor is really the way to go. My current monitor of choice is the BALMAR SG200. There are other threads on here why I think it is the best choice. It also works well with the carbon foam batteries.
A couple of things with your drawing, you show the KISAE DMT1240 output going to input of the MRBF fuse bar. two things wrong there, normally you would run that from the battery and have a separate fuse that covers the battery to MRBF fuse3 block, It could be a terminal fuse, I generally put a class T fuse between the battery and any distribution.
You could use the now open position of (MRBF) fuse block for the KISAE, but the fuse block needs to be close to the KISAE to make this work, I normally don't go over a foot when I do this.
Now you need to look at your distribution, the STC blade fuse panel can take a maximum 125 amp fuse, generally most of us will never max out the fuse block so it is OK if you downsize accordingly. The problem you have is you are using a 60 amp terminal fuse, but downstream of the battery you have the 125 amp fuse and 40 amp fuse of inverter. More reasonable would be 125 amp from battery 80 amp on fuse and 40 on inverter, 80 + 40 = 120 which is less than the 125 amp battery fuse. The way you had it, the 60 amp from the battery would have been the limiting factor.
There is generally no problem in using larger wire, in fact most of the decision in wire size comes from voltage loss calculations. I have installed pretty much the same system in 4 Transits this summer, depending on your Transit, you might already have a 65 amp auxiliary fuse in in the seat. I have generally been just using terminal fuse, to keep my builds consistent.
You also will need to control the relay for the KISAE DMT-1250 input. There is a vehicle interface under the seat (right corner) that has low active sink, when the vehicle is in the Run State, it is pin 2 of this 8 pin connector. It is page 188 of the 2016 BEMM, this provides enough sink current for the relay, you would provide a 12 volt source for the other side of the coil. The proper thing to do would be purchase the mating connector, I generally have just tapped into using a posi-tap connector
I will try to fix up your drawing when I have a some more time.