Question about armholes

I am getting ready to start my first cardigan sweater and I need a little help. This child’s sweater has no armhole seams and it says “mark beg and end of last row for beg of armholes.” First off, how should I mark it and is the marking for the purpose of knowing where to pick up stitches further along in the project to knit the sleeves on? Secondly, they use
1 1/4" buttons and I am using 1" buttons. The button hole directions say work 4 st, bind off 3 st, * work 14 st, bind off 3 st and rep from * 3 times more, work to end following row, work in ribbing as established, cast on 3 st over each group of sts bound off on previous row complete same as left frontband. Should I adjust this in anyway so the buttonholes aren’t too big for my buttons? I am using the exact recommended needle sizes and yarns.

Thanks for your help!

You mark the beginning and end of the rows with stitch markers. You can tie on a little piece of yarn if you don’t have any ‘real’ markers. You’ll probably use these as a reference point to increase to create the sleeve stitches, since seamless sweaters usually have raglan sleeves.

Buttonholes are pretty stretchy, but it is possible to have them too big. You could make the buttonholes a stitch smaller if you want.