I have a pier and brick curtain house, crawlspace is encapsulated but with uninsulated curtain walls.
House mudsill (sitting on the brick) is approx 24 inches above grade in the area of interest, floor is 30-something inches above grade.  CZ3a, we don’t usually get snow here anymore.

I would like to add a small addition, an ‘L’ with 14×14 foot legs.  The roof will be a shed roof with a headwall transition, and will form the end of a breezeway roof to a garage (for zoning reasons).

One leg of the ‘L’ would be at the same level as the house floor; a floor structure with joists, etc., for a laundry/mechanical room expansion.
The other leg would be a transition from house floor level to grade/slab level;  conceptually a mudroom with a landing and a few stairs.

Is it a bad idea to attempt to add conditioned space directly next to a brick crawlspace curtain?
I’m stuck on foundation options, given the house-to-grade height transition.

One option may be a slab for the entire addition (stemwall and spread footing?), stick framed to full height, and butting up to the brick curtain wall at the wall bottom. Would have to air seal/insulate the brick inside the addition, because of the crawlspace on the other side.

I’m not sure if I should be worried about water movement through the brick, moving from the exterior side of the wall to the interior side along the same plane, bypassing the framed wall that will butt against it.  I understand that a surface seal can be done with liquid flashing or with kerf cut flashing and gunned sealant (similar to brick chimney flashing), but not sure if that’s sufficient to stop water….?

If the height transition, material transitions, insulation/sealing etc. with the existing brick are too problematic, I may only do the laundry/mechanical expansion as a crawlspace extension, and scrap the mudroom area. The mudroom would then be replaced by a porch, also covered by the breezeway/laundry roof continuation.

Quick mockup attached with the existing first floor, above the crawlspace.
Mudroom in blue, laundry/mechanical in purple.  Some doors and windows would get deleted, etc., so ignore all of that.