Is my homebrew feat “Healing Adept” balanced?

I’m playing D&D 5e in a group that has many years of experience with older versions of D&D but is new to 5th and our GM is new to being in charge. He has allowed feats (upon approval) and I wanted to make my healing more effective. If there are any official source feats to improve healing, I couldn’t find them. D&DBeyond has a great many published homebrew feats, but between the GM and myself, we declined the majority of them for being either overpowered, underwhelming, or poorly written/exploitable. However, there were several very good ideas buried in the details, so I tried my hand at writing my own: Healing Adept.

Prerequisite: Ability to cast at least one healing spell, WIS score of 14+

After long practice, you have become especially adept at magical healing.

When you cast a healing spell with variable results, first roll a d10. On a roll of 10, your spell heals for the maximum amount.

You may add your Proficiency Bonus to your Spellcasting Modifier for healing spells you cast.

If an ally within 60 feet of you would fall unconscious due to damage, you may use your reaction to cast Healing Word at 1st level without expending a spell slot. This spell must target that ally. You may do this a number of times equal to your wisdom modifier (Minimum of Once).

You recover all expended charges after a long rest.

After working with other members of the group who have experience with GMing and "Rules-Lawyering", I came up with the above. I tried to be both precise and concise in my wording to avoid any potential abuse. On review, our GM was unsure about one specific aspect:

You may add your Proficiency Bonus to your Spellcasting Modifier for healing spells you cast.

We discussed the PB adding 2-6 points (level-dependent) of flat bonus healing, and he wasn’t sure that the amount is balanced. To Be Clear: He deferred judgement on the feat as a whole, stating "I do not want to allow something then realize it is overpowered and have to take it away."

So on to the question
GMs: What would you add, remove, or adjust before allowing this Feat at your table?