I have a master keyboard with only usb-to-host midi out. How can i connect it to montage stand alone or through computer? Thanks.

Through the computer... you’ll need to consult the documentation for your master keyboard for information on if it requires a driver or how it communicates to your computer. You can use a computer utility to Receive it’s MIDI coming In, and route it on to the MONTAGE.

The MONTAGE can connect to the computer via USB “To Host” port. It uses the “Yamaha Steinberg USB Driver” for both MIDI and Audio communication.

Can i Connect - USB keyboard to MIDI gear -WITHOUT A COMPUTER - with this little Box -USB to MIDI Adapter- called
a)- Kenton MIDI USB Host MkII - (Your USB device is plugged into the USB MIDI Host mkII instead of into a computer. It provides MIDI In & Out sockets for USB MIDI keyboards and controllers which have only a USB B type socket.)
b)- midiplus USB MIDI Host)- (USB MIDI Host - let your USB MIDI keyboard connect to USB MIDI Host to have MIDI in / out Jack instead of connecting to computer)
c)- miditech USB MIDI HOST - The USB MIDI Host is MIDI Tool to Convert MIDI Data from an USB MIDI device to a normal MIDI device with the 5pin DIN MIDI port. Connect your USB drum trigger pad, USB controller or USB MIDI keyboard to the USB MIDI host. It will get power from the USB MIDI host device and convert all incoming USB MIDI data and transmit it to DIN MIDI port.
Source: https://www.soundonsound.com/reviews/kenton-midi-usb-host

Yamaha has suggested Kenton for similar requests.

https://yamahasynth.com/ask-a-question/midi-controller-direct-connection-to-montage