Today while configuring a new BGP, I setup the peer before the filters. Next thing I know, my entire network is down. Took forever to fix.
The problem was that my OSPF on a downstream router was set to redistribute BGP routes. I realize that putting 620,000 routes into
every route is a bad idea.

Is there a best practice to keep this from killing the network is the same mistake happens again? Should I setup OSPF route filters
that only accept my IP ranges? If I add a new BGP customer, do I have to go through and then update every router?

What is the "proper" way to set this up that doesn't involve updating every router every time I add a new customer?

As default never put up OSPF to redistribute BGP, if you need "FULL" feed down you should use iBGP (internal BGP)for this.