We have a CentOS 7 RPM repo for Suricata 6.0. Please see Guide: Suricata RPMs for CentOS and Fedora.
This only depends on packages that are in the base distribution or EPEL and will still use Python 2 on CentOS 7.
You do not have to upgrade to Suricata 5 first as Suricata does no automated migration of configuration files. So you can save yourself some time by moving directly to 6 and manually updating your configuration files. See 4. Upgrading — Suricata 6.0.2 documentation for more info what may need to be attended to.