its worth watching a few you tube videos to get a basic feel for setup
Racks are easiest but not a flexible as songs
if your just using the same keyboards and will not change them the rig manager may not be so important
Think of racks as fixed songs where you want to have a few variations of the buttons on front of your rack but not switch racks in the song
Think of songs and song parts where you want to switch variations on a rack but also switch to completely different VST racks in song parts. This is what I use, as I often switch Between piano hammond strings solo instruments, and have multiple splits across both keyboards ( and Keytar)
look at global rackspace to have your final audio output cleaning, Main mixer, compression, limiter, eq, Routing.
Eg i have a final mixer whare i can adjust the volume to the FOH or PA and have eq comp and limiting set here so I can have a more optimised sound to PA, it also allows you to route things like mono / stereo / IEM stage monitor etc I also use the SAFP for backing and clicktrack here to mix into the IEM / Stage Monitors.
I use Streaming audio player for backing and click track, as well as effects example sample of intro to us and them then into keyboards.
You can use the midi player but it depends on how good your midi playback vst is, the only decent one i found is halion sonic which allows general midi sounds playback, but you can use vsts eg Kontakt and route the midi player channels to individual layers in Kontact to get realistic sounds.
start simple, find the hardest song to do and build racks / songs and parts around it, add another song and test before duplicating to many songs too fast. a bit of time at the beginning getting things right can help same time going back and reworking tons of songs later.
f you dont have a foot controller its worth buying a cheap one to start with
If you have bluetooth midi this is a cheap starting point
M-VAVE Chocolate BT Wireless MIDI Controller Rechargeable Portable 4-Button Foot Pedal with APP Control for Musicians and DJs
about @£25 on amazon
Good luck, Its a product and a great journey.