Need Help for Newbie configuration with Multiple Wan & SSID

I'm pretty new here and sorry first if language is not the good one

I have 2 routeurs with OpenWrt (1 main routeur & 1 acting as AP) and 2 physical Connection to internet (DSL+cable)

I would like to setup my network with some more options than the basic one and I need some guidance...

I have 4 way of connecting to internet (2 physical and 2 "virtual" using the 2 physical)

  1. DSL Modem (Dynamic Public IP)
  2. Cable Modem (Dynamic Public IP and not stable connection)
  3. OpenVPN
  4. OpenMTCProuteur with a VPS to have balanced line with Fix IP but with limited bandwith

What I would like to do is being able to have device of my home network :
==> using one of the WAN connection regarding the SSID they are connected
==> for wired one using policy or rules
==> but staying accesible between each other (media Sharing)

I'm currently trying with Mwan 3 and My first idea is to make different subnets and assign each subnet to a Rule.
Each Rule will link to a policy of using a set of wan

My questions on Local Network organisation to have different Ip Range that I can use in the MWAN3 rules
A/ How to organise local Network ?
Should I use VLAN, with Different DHCP range that each one is link to a Wifi SSID
Should I use other way of doing it
How could I be sure that each ip Subnet is able to reach other subnets (is it bridging interfaces?)
How to act with Access point to have the same SSID used by the same routeur and good roaming

This is certainly not so difficult, by I would be happy to have some guidance

Thanks in advance for help or link to tutos... of similar