We need a  Firewall+VPN+Load Balancing router for the above links, but we're not sure which of the 29xx series would be the best fit.

Any suggestions welcome, please.
 

The obvious choice is something from the 2927 series.

https://www.draytek.co.uk/products/business/vigor-2927-series

With the benefit of hindsight, I suggest you think about WiFi and other requirements and make a selection on that basis.

I chose the Vigor 2927ax because it was the obvious upgrade from my 2860 but I think I might have been better to have gone for dedicated WiFi access points and bought a router without WiFi.