You work in an Internet Service Provider with only 300Mb to the internet? Anyways, are you going to be providing internet to business and home, what kind of "last mile access" do they have? Is this like a co-lo ISP? You might be able to get around with 6509s with a supped up supervisor, I don't think you would need to go through the the ASRs XR or even 7200s those can do crazy amounts of bandwidth. What about firewalls?