Please help me to coect my external hard ware synths to studio one

I am a total novice when it comes to technology. My studio at the moment is my Keylab 88, ruing through a Safire 6 Focusrite, into Studio One. I have a very large number of VSTs, including Omnisphere, Complete 11 Ultimate, etc, etc. However, I now want to coect my hardware synths into my set up, as I have not touched them for years. Here is what I want to do.

Have my Keylab 88 ruing my VSTs as I do currently.

Have my Nord Lead 3 keyboard ruing all my external hardware synths, which are Nord Lead 2, JD990, Supernova 2, Kawai K4r and a Proteus.

I used to use an Audio with my Atari set up many years ago and I was able to give each synth a Port, then use that port to maximise Multitimbral function. So, 4 tracks in one port for the Nord Lead 3, 4 tracks for the Nord 2, 8 for the Supernova, etc.

If I buy an Maudio 4 by 4, can I link them all through that and into my Studio 3? I've totally forgotten how to ensure the sound also comes through. I have a 24 input ********* mixer. Do I run all the synths into that then auto them into my iMac? Can I use the Safire 6 USB to do this even if it is ruing the Keylab or do I need to get another one?

I've looked on youtube but I can't find anything that helps me do this. I would really appreciate a schematic from someone or some detail on how to accomplish this.

Also, once I have recorded a sound onto my track in Stdio one, does it playback independently or do I need to ensure the sound is assigned to that track overtime I set up my track?

Many thanks and apologies for my probably very basic question.

David