Tony,
I’m glad you are enjoying your first experiences with Dorico. You obviously have long-term experience working with notation software but if, like me when I started with Dorico 2 years ago, you have not had cause to use the MusicXML format before, I suspect your experience with importing your Sibelius-generated file would have been more trouble-free if you had exported it from Sibelius in MusicXML format and imported that into Dorico rather than a midi file.
Also, if you are not already aware of it, Dan Kreider has produced his wonderful A Beginner’s Guide to Dorico. which can be viewed on-screen or downloaded and printed as a pdf document at the link below. I find it very helpful to have close-by when working with Dorico.