That is an interesting option. I wonder what RB#2 WAN settings would be though seeing as every address in the subnet will be routed to me ... What would the gateway address be? and would WAN be a /32?
I cannot see any advantage in replacing one SPOF (the "existing" 'Tik) by another SPOF (the "cheap dump GbE switch") except that you have to buy, physically place and feed another box. I don't know how accessible the location is, but putting two ports on each 'Tik into a WAN bridge and interconnecting them by a cable would essentially do the same service - if the port to which the fibre modem is connected goes down at one 'Tik, or that whole 'Tik goes down, you can ask a trained dog to connect the cable from the modem to the other 'Tik and the service is re-established.
The above applies if the two public subnets (your existing one and the new one) exist in parallel on the physical media as I've assumed before, i.e. if you could configure any of the two subnets on a 'Tik connected directly to the cable modem and it would work. But the following suggests otherwise:
The Public Addresses I will use for the second router is completely different as far as addressing goes, and I can get anything from a /30 to a /24 (e.g. 18.104.22.168/29) routed to me down the same service and I can do with it whatever I choose. The current WAN addressing of router #1 will not change in any way.
English is not my first language so I may understand it wrong, but "routed to me down the same service" suggests that the ISP would use the existing service as a connection subnet for the new subnet, which requires a router functionality at your end too, and in such case, the existing 'Tik would have to route the traffic of the new one. So this point is the one which needs to be unambiguously clarified with the ISP as it determines which of the two configurations has to be used at your end.
To make the picture complete, do you have an optical SFP in the existing 'Tik or a separate optical media converter with copper GbE port on the local side?
Instead of writing novels, post /export hide-sensitive. Use find&replace in your favourite text editor to systematically replace all occurrences of each public IP address potentially identifying you by a distinctive pattern such as my.public.ip.1.