Better, not Perfect way to Insulate Uninsulated Attic Space in older Home
Going from no insulation at all to some insulation is indeed going to pay back, and will pay back faster than more insulation - going from R1 to R10 saves you ~90% - going from R1 to R50 saves you ~98%, so the difference between R10 and R50 is only saving an additional 8% over the R1 case, even though it's saving ~80% over the R10 case.
...so some IS (much) better than none.
Get rid of the K&amp;T.
What you insulate with after that is up to you. Batts are conceptually easy, but my looking into choices has shown a fair amount of issues with air leakage around the edges of batts, and things like the lap joint shown in the third picture cause issues, as will any other non-standard spacing. You can fuss with cutting batts to try and address those, or you can go with some form of loose insulation, such as cellulose blown in that easily accommodates irregularities in spacing and framing offsets. Foam (board or spray) tends to be relatively high priced, though it can fit more insulation (value) in a fixed space. Save it for where that matters to you. In the attic you can usually just pile more on unless you are trying to have a floor up there.
Opinions vary and are stridently held, but cellulose may also remove the need for a vapor barrier, according to some sources. If your climate is primarily heating, vapor barrier (if used) goes next to the ceiling. If primarily cooling, on top. &quot;The warm side&quot; on average.
For what you want to achieve (30% savings) you can probably ignore the small sections of dormer and avoid ripping plaster for now. Do the easy parts first. Come back to the rest later. And yes, do consider hiring the job out, it may not cost too much more.