By 'have a launch page' do you mean that when the learner clicked on the course title in the LMS it would launch, say, 'launch.html' (this would be set in the manifest file) and then that launch page would have a launch button linked to Adapt's index_lms.html?

Pretty much, yes. It actually tries to open Adapt's index_lms.html automatically. The link to do so is there as a fallback in case of popup blockers. There's an example here.

I also see there's adapt-launchNewWindow extension. Haven't had a chance to try it yet but does that do something similar?

Yes it does and quite frankly I would go for this option.

Finally, I looked at iOS-scrollFix this morning and it requires a patch in Trickle's .js and LESS files. Those Trickle files seem to have been completely re-written subsequently so the patch instructions are out of date and unuseable.

Which patch instructions?