Hello there!
Monk finishers and multiclassing/metamagics are an odd one.
Empower Healing (or any other metamagic feat) does *not* appear to affect Healing Ki, however your Life Magic enhancements,and item-based spell boosting items will help. Of particular note are Superior Ardour potions - extensive testing with Healing amplification builds has revealed that Superior Ardour I potions actually give 75% boost instead of 50%.
Note that Healing Ki and fire finisher count character level instead of Monk level (in spite of description).
As to taking a Monk or Cleric level for level 4 - I would lean towards having the Monk level, but you might not need Finesse yet. Toughness, or Power Attack (with a +1 str tome, or level up point) may help more, as you should have plenty of to-hit bonus available for the enemies you are facing.
As to the second level of Monk - it is a question of whether Evasion is worth having to invest in scrolls pretty early on. If you know the quests then you can probably make it through any traps you might find up to level 12. However if playing with random groups odds are you will need Evasion sooner.
If mostly duo-ing with your GF then you need not worry about a 3rd level of Monk (at least put off such a choice until after Cleric 11) as you can rely on her to bust out the light buffs
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If you are ultimately planning 3 Monk, I *really* recommend putting a point into Str from somewhere, because Power Attack will help make sure you are getting Ki from your hits. Stunning Fist might also be worth considering, though eventually it becomes ineffective.
Unfortunately specializing for Spell-Penetration on a Cleric-Monk can be difficult - not just due to the level gap, but because the items most commonly imbued with Spell Penetration (sceptres, daggers etc.) would break your monk stance. You can use a quarterstaff, but would have to be constantly switching between your spellcasting weapon and melee weapon. Spell Penetration Kamas do happpen, but spellcasting Kamas are relatively rare (in my experience). Shattermantle Monk weapons are more common - combine one of those with a Cursespewing kama and you can rock out some un-Heightened Soundbursts...
So on your spellcasting path I would consider swapping Spell Penetration feats (or the TWF/Finesse feats) for double focus in Evocation, or one of the Spellpoint feats and Heighten.
On your melee path, I would drop Extend for Power Attack.