While some content is outdated you should find my newbie tips of value –
Onboarding steps for Xert trial users and newbies - General - Xert Community Forum
I can circle back to address some of your other questions after my ride today.
If your rides without power include HR (and preferably cadence too) you can enable HRDM under Profile Settings, General tab.
There is a massive glossary that explains many of the nitty-gritty details but I hesitate to send you there. 