If it were me, Can't say I'd be that interested unless the job was on my door step! You'll be fine. Use a powdered adhesive, go for a plastic edging strip rather than ali, and get one that's a good few millimeters deeper than the tile to allow for adhesive, e.g. if the tile is 8mm go for a 10mm profile.
Hardi should be mechanically fixed but also bedded onto adhesive, (according to Hardi's website), so removing it will be no easier than removing tile. As I said, you'll also see the sieds of the board as the edging strip will sit on top of it. As the board is 6mm, and I'm assuming the tile will be at least 8mm, you'll need an 18mm edging strip and I think the biggest made is around 15mm, (although I stand to be corrected on that!).