If we have single IDP configured, You just need to adjust the 'path' in SAML config to point to other sites.  If we have multiple IDPs, adding new config would make sense then.Accordingly, you can adjust you rewrite rules, resource Resolver or etc/map configs so that once it goes through the  dispat...

These error message suggest that there are duplicate loggers defined for a couple of classes. If you can navigate and login into Felix console, Go to Configurations and search for logger. open them one by one and see which are duplicates and delete if any.If you are not able to login into any consol...

I am not aware of any workaround other than installing latest patches for 6.3. Also, I wouldn't recommend putting patches/fixes directly on production but test it on lower environment and promote it production in a systematic approach

Moving to latest maintenance release for 6.3 should help here. Plan with your team to update the instances to AEM 6.3 SP2 CFP1

I didn't get the complete issue ? Are you referring to users/groups being added using the Classic UI or Touch UI or you don't' see the users/groups in CRXDE ?Which exact patch version of AEM 6.3 is this ? If on less than 6.3.1.2, there is a known issue  where Updating a group with more than 26 membe...

Uninstalling SPs and CFPs in not supported. Please perform a backup before you install Sps and CFPs in environment and later sanity test to check  if everything works well or not

in addition to Oauth, for the data later part, content fragment models would be a good option to get all the data as json and just parse and use it in external applications

config looks good to me and assume the SLO url was used in the saml config. Apart from that not sure, what could be it. If you aren't able to figure out, Raise the concern with Support and someone can look at it dedicatedly on this.

Dispatcher does nothing extra but acts like a proxy with other features(filters, cache) specific to AEM so not sure how APM would be helpful here.

See (1) for detailed information on how can set it up(1) : Monitoring AEM With New Relic - Blog - 6D Global