Looks like bootloader will support booting from tftp, assuming you can find/make an image for it.
But this line Verifying kernel signature... makes me think its probably a lost cause, since i dont think there is any way to satisfy that check . The only way would be to rewrite the bootloader which is not a trivial thing to do..
Instead
Id suggest getting a good device (8+ mb flash / 64+ mb ram), and running it as a client of the isp’s device.
(Isp’s router) lan1 == wan(your router)lan ports/wifi
- Its true youd probably be running with double nat , but it shouldnt be a deal breaker unless youre wanting to do something fancy.. the performance should be good enough. (Test connecting directly to isp router, and then with the openwrt device inbetween if you suspect any speed problems.)
- this approach separates your internal lan devices from the isp
- you could set up a vpn on your own opwnwrt device and tunnel anything that the isp is blocking (but if they are id strongly consider going with another isp)
https://openwrt.org/docs/guide-user/network/integrating-lede-introduction
https://openwrt.org/docs/guide-user/network/switch_router_gateway_and_nat
Edit: adding this awesome top10 device summary by @slh
Top ten routers currently in use?