Each ornament will be 35 x 35 stitches - how big that ends up really depends on which fabric you decide to use for it, as on 14 ct Aida it will of course be bigger than on 40 ct linen.
Each ornament will use 3 colours - for the patterns I have decided to use the birthstone colour of the month as the starting point, however if you decide to use another colour, use metallics, variegated thread etc. it's entirely up to you and will make it uniquely yours.
You do not need to sign up for this SAL but if you do use any of the patterns I would appreciate you dropping by my personal blog: Magical's quilts and more... and posting a link to your photo or blog post in a comment on the page of the month that corresponds to your finished ornament so I and everyone else can admire your work.
This means that you can start at any time and perhaps binge stitch them all in December or do the first 6 as a Christmas in July project - it's entirely up to you!
I will post the patterns on this site on the first Friday of the month so that you will have a weekend to work in if you are stitching along with the rest of us.