Lots of newbie tips are posted in this thread including answers to some of your questions –
Beginner questions - Support - Xert Community Forum (xertonline.com)
Your Status Stars count is tied to your training load (TL) which is controlled by the improvement rate (IR) you set under Goals.
As your TL increases (hours/week and intensity) so will your star count and in turn the diamond count for recommended workouts.
Base phase is endurance focused regardless of selected athlete type but harder workouts will appear halfway through build into peak phase as you approach your TED.
However, if you selected an athlete type in the endurance quadrant then recommendations will cluster towards endurance throughout the phases. You can mix things up by using Filter and changing focus duration to another quadrant such as Climber, GC, or Breakaway Specialist.
Hopefully you can increase your TL before your event as hours/week is the major factor in increasing your status stars count which in turn boosts diamond count for recommended workouts.
If you aren’t sure your fitness signature is correct you should select a breakthrough (BT) workout from the library and ride that in slope mode to confirm.
A gradual decrease in TP is normal (due to decay) if weeks go by without BT events occurring during rides or workouts.