You will want to use a larger needle size than your piecing needle, probably somewhere between a 14 and an 18. I started a test of types of needles (denim, topstitch, etc.) but I didn't find much difference between the different types and then went on a sewing break of a year+ while selling our house and moving so I'm not remembering much of that..
As for stitch length, that's more of a personal decision. For me it a combination of the fabric and batting and personal taste, I can't really give you a stich length other than "longer than you piecing stitch". You do have to watch out for when you get large portions of the top bunched up that you are still moving well and keeping your stitch size reasonably consistent.
First project is usually a bear... again, practice and the more you do will help. So do your best and cut yourself some slack if things are less than perfect. We are so close to our work that we are aware of every little bobble but the child (and probably the parents of the child) won't be aware of any imperfections
