Used this site for Tubular Cast On: https://www.purlsoho.com/create/long-tail-tubular-cast-on... --> translated this into line drawings and a downloadable pdf here: https://belvederebiaise.files.wordpress.com/2018/01/tubul...

On 3.75mm needles, I did not get gauge when blocked, so making size S should be okay (as I would fit XS).
For raglan increases, I knit to 2 sts before marker, kfb, k1 through the back (twisted), slip marker, kbf.
After raglan increases, I knit 16 rounds (instead of 10) without increases. In hindsight, it might have been better to spread some of the increases out, as there’s a bit of a weird bulge from the straight knitting (this mostly blocked out).
I knit three balls of yarn on the body and one on the first sleeve (though I did block the body so far, but not the sleeve).
I wanted to add a bit of shaping to the body so after 25 rows, put one decrease on each side of the body. I repeated this every 6 rows, 7 times total. After decreasing on the body, I knit 22 rows straight.
Knitting the sleeves, I used metal dpns and I knit 80 rows before starting the decreases, which I centred opposite the garter stitch panel. For those, I did k1, k2tog, k to 3 before end of round, sl1kwise, k1, psso. Due to my gauge, I knit 7 rounds even between each decrease, and did the decreases 8 times (64 rows). I almost finished the ball of yarn and tried on the sweater and the sleeve seemed long enough. However, measuring against another shirt, I should make the sleeves 18.5” long and according to my blocked gauge, the sleeve would only be 15 1/8” long now. So I could knit an additional 2” or 17 rows. The neck ribbing has 13 rows (+2 rows of tubular cast on). -After trying the sweater on again, the sleeves are too long, so I frogged back to 142 rows and started the ribbing while incorporating the last two decreases. 13 rows of ribbing were knit and then tubular/kitchener cast off was used.
I picked up the body again and knit two more inches on it while incorporating two increases every 5th row. On the start of the first row of ribbing, I incorporated 5 decreases equally around to slightly tighten the ribbing edge.

The size is good (my bust size is <32”).
When I wear the sweater, it comes up too high in the front for my liking and I would have been better off casting on less stitches and increasing until joining, as suggested by Karen Templar in the Improv top down sweater suggestions.