Hi, I just took time to look at this pattern and make a tiny hat with 30 stitches and do the decreases to see how it works. As far as this question goes,
When I P2tog, should I purl another before starting the K3, or not?
I think you could purl that stitch or knit it. It says if there are not enough to do a repeat to knit them, but in this spot where you can still keep it in pattern right there I think it could go either way as long as you are consistent the rest of the hat.
Your first decrease comes on rnd 2. P2tog and either P1, K3 across or P2tog, K4. And then begin a new 5 st pattern repeat across to the next marker.
Now in rnd 3 when you come to the places where you decreased you only have 4 of the 5 stiches for that pattern. So on rnd 3 I think you could P1, K1, YO, SSK. Or you could K2, YO, SSK. Or you could just work all 4 in st st. I did it the second way in my trial.
Rnd 4 would be another dec and you would be beginning with 4 sts. P2tog, k2 work to the next marker and do the same.
Rnd 5 is another rnd 1 and worked even. You only have 3 of the 5 now so knit them.
Rnd 6 another rnd 2 and dec: P2tog, K1 then begin the regular patterning across to the next marker.
Rnd 7, another rnd 3 and even: You are down to only 2 sttiches. K2, pattern across to next marker.
Rnd 8, another rnd 4 and dec: P2tog, begin a new 5 pattern repeat and work across to the marker and repeat.
Rnd 9 another rnd 1 and you have only 1 st of the orginal 5 st pattern to work with so you have to begin borrowing from the next 5 st rep. P2 tog, P1, K2tog, YO, K1.
Now you have 5 again on that repeat because the P2tog counts as the first purl (1 of them is the last st of the last 5 and the other the 1st st of the next 5). of the purl 2. So you begin doing the sequence again like we did it the first time beginning the next decrease rnd.
So begin at the top again where you are decreasing on rnd 2 and have 5 stitches to work with when you begin the decrease. I think that is right and will keep everything looking nicely. Let me know how it went. It has been 2 days since you posted this so maybe you have already finished the hat before I got this done. LOL