Shower Waterproofing

Here is my second post, this is for the bathtub surround.

I have two young kids who love to take long, steamy showers; and have an affinity to get water everywhere. Considering extending the tile around the sides of the tub 4"-6" to help keep overflow / splash water off the wall.

Hall Bathroom Tub Surround:

Space: Standard 30"x60" tub alcove. Height veries with sloped ceiling, but averages 12.5'. Acrylic Kholer 30x60 alcove bathtub installed, entire bathroom including alcove covered with greenboard drywall. Entire space is painted - this unfortunately includes the alcove... didn't catch them in time (PVA drywall primer, Behr semi-gloss 'bath/kitchen' paint). Plan to tile alcove to approx 10' from floor. Floor is polished cement slab.

Penetrations: 1 tub valve, 1 shower head, 1 tub faucet.

Waterproofing Plan:

Prime alcove over existing paint with bonding primer.

HydroBan membrane on alcove wall; affixed with MS sealant (or would thinset still work?)

HydroBan tape wall-to-wall plane changes w/ ALL SET and MS sealant to tub flange.

HydroBan collars for valve, shower, faucet.

Finishing Plan:

Metal tile edging around perimeter.

Mesh backed small subway tile sheets (12"x12") with ALL SET

Polyblend PLUS grout (Not set on this product)

Color match grout caulk in tile-to-tub transition.

Fixed shower curtain rod.

My main concern here is the painted wall, I really don't want to cut the drywall out if I can at all avoid it. If gluing the membrane on isn't a good solution I thought about using a thin 1/4" HydroBan foam pannel in lieu of the membrane and trimming it out with a deeper 1/2"-5/8" edge trim.

Any suggestions on plan or materials is appreciated!

Thank you,

Aaron Meyer