Disciple of Life improves the recipient's healing

A qualifying spell of 1st level or higher restores its normal amount, then gains the additional 2 + spell level healing from Disciple of Life.

Blessed Healer heals the Cleric separately

From 6th level, if that spell restores hit points to someone other than you, you regain 2 + spell level hit points. This is not part of the target's healing roll.

Supreme Healing maximizes dice, not every numeric bonus

At 17th level, the dice that would be rolled to restore hit points use their highest possible results. Fixed bonuses such as Wisdom modifiers or Disciple of Life's 2 + spell level remain fixed bonuses rather than becoming additional maximized dice.

Preserve Life is not a healing spell

Preserve Life is Channel Divinity, not a spell. It therefore does not trigger Disciple of Life, Blessed Healer or Supreme Healing merely because it restores hit points.

Self-healing has a limitation

Blessed Healer requires the spell to restore hit points to a creature other than you. Healing only yourself does not trigger the self-healing feature.