Router openwrt Zerotier questions

Hello all,
I succeeded getting zerotier working on a slow router with openwrt, but I love more performance and still got a little issue. So 2 questions I got:

1: I want to upgrade the router with stronger cpu. After lots of googling and research only the netgear r7800 seems the one with openwrt to get. I was surprised because it’s a device 5 years old. What other routers compatible with openwrt are recommended with zerotier? Are the cores important or the single core Mhz speed?

2: And the second question is: zerotier on the router somehow doesn’t stay alive. It stops working somehow in a few hours or half a day. How can I keep it alive?

Thank you for reading and possible answers!