What is Required configuration of AWS server have 3+1nodes in Percona XtraDB Cluster 8 with Ubuntu?

3 node cluster setup and 1 separate RD backup  as slave with  1 node of cluster.
total 4 servers.
Database size  around -  200 -300 GB
Number of consistence connections/users could be - 300+

2 cores with 3 GB ram will be enough on each server?

2CPU/3GB RAM would be enough for a small testing environment. You should go for 16GB or 32GB of RAM for production.

Thanks @matthewb