So I, join the shoulders. (Which is the best way please?)
Then transfer the stitches from the holder to the needles. Do I then do the cast on stitches first, then treat the stitches from the holder as if I am knitting normally and do the increases just as I go along the stitches which were on the holder, before casting on more at the end of the row as well.
What is the name of your pattern and designer?
If you have sts on hold for the shoulders you could use 3-needle bind off. If not you can use mattress stitch or a sewn backstitch to join.
For stockinette stitch see especially after 2:25min in the video for joining casr off ends.
Begin by casting on the given number of sts for your size (24 for the smallest size).
If you can knit from the holder sts at the back of the neck (use the holder as the left hand needle) then that’s easiest. If not, transfer the sts to a needle and then follow the directions to work those sts as:
k3 [4:3:3:3:3], m1, (k4 [4:5:8:8:9], m1) 6 [6:6:4:4:4] times, k4 [5:3:3:3:3],
Finally, cast on the additional 24 [25:27:27:27:27] sts.
For the smallest size that’s 24+31+24+7=86sts.
Good for you for venturing into your first hood! Let us know how it’s going.
If you use the knit cast on you can use the first stitch from the holder (transfered onto your needle as you said, I do that because I don’t like working off a holder) to work into for your first knit cast on, it doesn’t work the stitch but works into it. At the end of the row after working the held stitches you can turn and use the knit cast on again to add the final set of cast in stitches.