I'm wondering what upgrade options people would commonly have
the builder installed for them, and what they'd do themselves
afterwards.

If you do afterwards, would you hire someone (e.g. from Home
Depot, or Lowe's) to help, say, on overall design (e.g. from
blinds, adding doors, full-length mirrors, lighting fixtures)
and on installation.

Considerations here a
1. Cost - which is cheaper (slightly or significantly)
2. Convenience - which one(s) would cause noticeable inconvenience
if done afterwards
3. Results/Quality

Thanks,
Raymond