BQ25895: Porting existing design to TUSB320 + BQ25895 - Need help to understand power path

Part Number: BQ25895
Other Parts Discussed in Thread: LM2596, TUSB320, , BQ25985

Tool/software:

Hello,
my board currently has the following power stage:

  • LM2596, to drive main +5V rail from external 12V battery
  • LM2735X, to drive main +5V rail from internal single cell LiPo 
  • (Microchp) MCP73843 as LiPo charger when device is externally powered, either from 12Vbat or USB-C
  • USB-C port, CC pins are SW managed by host MCU to work as DRP, only basic host/device functionality, with Rd=5.1k and Rp=56k.
  • TPS2065CD-2 to power USB-C Vbus in OTG mode
  • TPS2042D to draw power from USB charger
  • there is a mechanical relay which electrically insulates the LiPo cell when the device is powered off

Aside from the relay, components were chosen because easy board repairability was the target, and all these packages can be easily reworked.
The focus has now changed, and i am tasked with adding USB Fast Charge to the device: the current approach is too clunky, and since i'm now allowed to use VQFN/WQFN packages i started looking for pre-made solutions: i am leaning towards the combo of TUSB320 + BQ25895; i want to drop the hassle of managing the USB-C state machine, and use a USB-compliant IC that autonomously negotiates the correct charge current (i.e. the fastest available, reported by the USB charger).

I would prefer to have this working without I2C, using chips that i can drive trhough GPIOS; i will do I2C it if there's no other choice.
I need USB2 D+/D- data lines working with my HMI device; USB3 SS lines are unused.

The question: of all the parts mentioned above, what gets replaced by the BQ25895 alone?
The two load switches can go, as OTG mode is handled internally by the 25895.
The 25895 is a battery charger, so obviously the other charger can go.
But If i understand correctly, PMID output will be my new +5V rail driver, when powered by internal LiPo cell, so now even my 2735 boost can go? And why does it say "5V at 2.4A OTG" in the Typical Application schematic on the PMID pin, i thought Vbus for OTG would be provided to the USB-C port through the VBUS pin.

Finally, i can't wrap my mind around where exactly to connect the +5V supply coming from the 2596 buck converter: in the current setup, it's parallel to the LiPo boost, since that is disabled when 12V power is present, but with the 25895, i assume if i power the PMID line from a different source, it won't be able to use that to charge the LiPo, am i correct?
And i fail to understand if it could be connected to the output of the switching regulator on the SW pin, since the Typical Application in the datasheets suggests SYS from 3.5 to 4.5V.

Is it even possible to add a second power source, in a device employing the BQ25985?

Thanks,
Luca