Hi, yes you are right, there is alot to cover / so many possibilities with this much gear…
First of all, there are three main connections you have to think about:
Audio
Midi (via DIN-Plug)
and USB (which can be only MIDI, or Audio and Midi combined)
I suggest you make a little drawing (maybe only in your mind, if you can handle it) where you think about which routings / functions are important to you.
some hints:
there is , of cours, no best method
do you want stand alone operation or do you work with computer always on? (you could handle audio/midi routing via DAW)
If you want, you could, for example route audio from Sub37 into DT keys into ARII and also connect them via midi for complete stand alone jamming with audio and midi sync…
if you work with computer you can of course easily route your launchpad to one or all devices
you do not need overhub for experimenting… best thing would be physical usb sockets for each device directly on the machine…
in therory, the elektron usb connections handle audio and “midi” (sync via special Overbridge protocol) you could get all seperate audio channels or only the master channels of the elektrons into DAW this way. Also sub phatty can be grabbed on its own channel via DT keys audio input, I think - so at this point no need to upgrade your audio interface.
I strongly suggest to get familiar with the gear, before buying anything new 
maybe it is also a good idea to start with small sections of the setup and than add on top…eg get ar working with OB, then the next device etc.
also have a search at the this forum, there are already many good setup topics… i guess you will find more infos, once you are in the process and get into specific problems…