Help validate Gold Pro setup before I buy?

Hi experts, before I pull the trigger on Gold Pro I am hoping someone can do a quick spot check that my setup goals will work ok.  I am modestly ok with networking but have big blind spots and don't want to get in over my head.

Main Goal:

-- I just want to do a better job at reducing the surface area for external actors to punch into my home network and sniff around, so I'm thinking that my main use case is for the firewall and blocking inbound traffic to my stuff. 

Existing Setup:

-- I have two ISPs: GFiber 8Gbit (GR6EXX0C) and AT&T 1Gbit (yes, I do want to preserve option for ~8Gbit bandwidth for various reasons)

-- Multi-WAN reference is to use GFiber as primary and AT&T as Failover, I would consider Load Balancing but I have certain rooms/devices that I would always want on the 8Gbit lines and I'm unsure about how tricky Load Balancing would be

-- I have an Asus RT-BE7200 / RT-BE88U WiFi router for my internal mesh and access points, (I use it with a backhaul to other wifi access points etc)

-- I have various 10Gbit switches that I use for Cat6e lines that fan out from the router

Areas that I'm unsure about:

-- In the Multi-WAN setup that I want, which devices manage the network IPs?  I have heard that the GFiber modem wants to always manage it's own IPs and doesn't play nice in "Bridge Mode" -- will Firewalla "Transparent Bridge Mode" feature work with GFiber? 

-- I don't really know what I'm talking about, but it seems like I should avoid a Double-Nat setup in favor of bridge mode, but again I'm not sure if it's even possible with Firewall and the GFiber device

-- I'm also not sure how the Asus router/wi-fi fits in... will this simply be running in a passthrough mode with all the networking IPs etc managed by Firewalla?

-- I assume my setup will basically need to look like:

---> GFiber & AT&T modems --> Gold Pro --> Asus & Switches

...does that sound right?

-- I do have various smart home devices etc that i would like to continue to be able to access remotely, so I'm not sure if all these layers and IP stuff will still allow me to access my smart home stuff remotely, are there specific policies etc that I'll have to set up?

What else am I missing, is there a better way to do this?