WAN redundancy beetwen WAN1 and subinterface

Hi, I have attached the .jpg to show You what I want to achieve(PORT 8 is in fact internal 1 interface). Default route normally must be through the WAN 1 interface. IF connection to internet through the WAN 1 interface do not work, whole traffic will go through MPLS and at the end to the internet. I have already checked this configuration ( but it didn't work): in the Router section -> static routes -> I added two default routes with different priorities after that in Router -> static -> settings -> I added link health monitor - from WAN 1 interface check the availability of 8.8.8.8 So, after that when I shutdown the connection through WAN 1 ( for example take out the cable from the interface) whole traffic should use second  default gw.

Is it possible to make redundancy betewen WAN 1 ( which is physical interface) and one of the subinterfaces on internal 1 interface (through one of the VLANs which is configured on this internal interface ? or just only between two physical interfaces ?

How can I shape the traffic on the second interface ( MPLS link is 20Mb/s and local internet is 30 Mb/s) ? Can I used Spillover for that or there is a better solution ?

 thx