1 - 2 gbps is sufficent
2 - block ports and protocols you don’t need, have some monitoring
3 - safer in what sense?
5 - yes
There is a limit to what you can with anti-ddos - if you get a ddos with 2 gbps (or more) then all the firewall rules won’t help you. then you have to talk to your provider to filter that kind of traffic.