Here is a thought about building a composing workflow.
In a band :
As a result we need a software to record midi notes from a keyboard : a sequencer.
I recommand Bitwig Studio : it’s easy to use ( at least not worst than the others) and multiplatform ( linux, windows, ios)
To edit parts, use musescore for the same reasons.
Arpeggiators permit generating drum kits, bass or guitar riffs, etc..
I haven’t got any special advice concerning the keyboard, just pay attention to the weight : more than 20 kg is heavy if you’re used to bring it everywhere.
Some devices called workstations can play on different midi channels.
Sounds are included in the device.
The sound card has to be present ( it’s very practical ) ; if not choose another model.
Some workstations propose a tablet to get the whole config, like the korg kronos.
Be careful the 88 hammer action version is very heavy.
Here the sounds are in the computer, as visual instruments ( VST ).
A sound card is needed.
This solution can be risky on stage.
A very insteresting solution : this is a ‘sound box’, you can add the keyboard you want.
There used to be the yahama motif rack-xs proposing this complete configuration, now it’s outdated.
My actual configuration is a Yamaha CP88 to have a good hammer action keyboard ( not too heavy ) and good sounds on stage + Nord Stage 3 compact ( lightweight keybed ) for organ and synthesizer. I use virtual instruments to compose, like Modartt Pianoteq for example.