Hey Eagle I would recommend window clips versus screws for holding the tub against the wall studs.
And I would for sure use a couple bags of Mortar Mix under the tub for added strength and improved feel under foot.
Have you seen some current post here on the process. Check out this discussion.
What Type of mortar under Acrylic Tub
Most tubs don't need the Ledger in place I find - the ones I work with anyway. If the ledger is not spec'd and you use clips and mortar I would think your good to go....