I will tell you, there is NO WAY to predict growth patterns. My boys were large (tall and heavy) according to the charts....by 12months of age they were all into a 24mo or more (my middle son wore a size 3T and size 7 shoes) but my daughter grew minimally and was wearing a 12mo and size 1 shoe at a year. By the time my boys were in 2nd grade, they were all in the smaller end of their age groups!
Bibs/no bibs??.....well that is a matter of taste and also whether or not you plan to potty train. Children are not able to take the bibs off as easily as "normal" pants, so, that decision is up to you.
My best suggestion is to plan on larger rather than smaller (children never shrink they just grow at different rates) and then purchase things as you either get a GREAT deal (so much so that if it is NEVER used you won't feel TOO bad) or as needed. Remember, in our climate, your child will most likely wear here winter outerware from Oct thru to April.....so, big in Oct could mean small in April......Good Luck!