If you want to pass the routes via a protocol - go for it.. But sounded like you wanted route the L2 at pfsense as well with multiple wans.. Ie 3 different wan networks on pfsense?
Without natting, or host routing that leads to asymmetrical traffic..
If you have a downstream router, you connect the upstream and the downstream via a transit network.. You don't just connect the downstream router to all the upstream networks via different wan interfaces.. That would be just a freaking mess.
If you want to use a routing protocol to exchange the routes - sure, but its complication for no reason. Not like the downstream router is going to be adding routes out of the blue and you will want to know they are down there via a route being added via the protocol.
And you sure don't seem to have multiple paths to gte to the downstream networks, and you don't seem to have need for a failover via loss of a path, etc. etc.
You could get as simple as using some large cidr on your top networks.. Say using a /20 which would give you lots of room for growth of more networks their, and then a /20 for your downstream networks, etc. But sure if you want to run bgp or something to play with - have at it.. Your still going to connect them via a transit network(s)..