Internet Service Provider core router

I'm looking into vendors to provide the core routers for an Internet Service Provider network. It is a new ISP with no existing infrastructure, building out a Fiber-to-the-Home GPON network with a green field to play with.

Initially, the pilot phase of the build will have approximately 6,000 residential and SMB subscribers, and we expect to hit that number in about two years from the time we light up customer 0. Over time, maybe 8 to 10 years, we hope to grow the number of subscribers to approximately 60,000 residential/SMB accounts and offer some more advanced services to larger businesses.

At onset, we envision having one core and add a second redundant core as we grow.

While we are open to any OEM, I am expecting the choice to really be between Cisco, Extreme, and Juniper.

If you were in charge of researching the core router, what questions would you ask the OEM to help select the right-sized router for the situation? What answers would you want to have ready when asked questions from the OEM? And finally, do you have a preferred OEM for providing core layer 3 functions for a growing ISP?

TIA!