Mainly it will just handle a few GRE-tunnels at 1 Gbit or more and be able to failover with HSRP.
Agree with what Joe said.
1 Gbps or more? That's already ASR 1001-X with a base "5 Gbps" license enabled. (Data Sheet)
Could the ASR-920 be a good choice or is the ISR series to be preferred?
Depends on your requirement. ASR920 is aimed at service provider.