Setting up firewall, managed switch. What are my wifi options?

I've decided to take on the project of setting up a firewall on my Telus fiber line but I have the added challenge of working within a pretty tight budget. 

I have the Tower/Trashcan router currently with several boosters and this works well enough for us. I'm trying to get a better sense of my options for setting up wifi. I thought it wasn't possible to set up a second wireless router because of double-NATing but I just read a post that said it shouldn't be a problem because Telus assigns internal IPs that allow two routers to operate at the same time.

Is that true? If so, could I buy a another, used trashcan (~$25 on FB) and use it as my wifi "hub" and continue to use the boosters I already have? Or is a second wireless router not viable and I'm limited to setting up ethernet-wired APs?

Thanks.