tools to gather variant information from thousands of servers and update into database
Doing something with collectd feeding into Prometheus or datadog is definitely a good idea for gathering metrics, but it doesn't help you with things like the kernel version.  Handling process monitoring might be better handled with nagios or datadog as well.  But for the bulk of what you're doing I'd say that it makes the most sense to stick with ansible.
What you're doing sounds very similar to the ansible-cmdb project:

Ansible-cmdb takes the output of Ansible's fact gathering and converts it into a static HTML overview page (and other things) containing system configuration information.
It supports multiple types of output (html, csv, sql, etc) and extending information gathered by Ansible with custom data. For each host it also shows the groups, host variables, custom variables and machine-local facts.


I've been using this for the last couple of years and it continues to evolve and improve.  I hope you'll find it useful as well.