First, depending on what you'd be embroidering on you'd want to measure the area then select a design. If you have design software you could resize it otherwise, do a test sample of the embroidery on the same type fabric and lay it out on the area. Hope this helps you.

What, you didn't like the 19 pound baby? LOL
Definitely depends on what you are embroidering on. I think tiny (maybe 1/2 inch) is good on a onesie. You want the fabric to stay supple and soft, not stiff from the design. But you could go larger on outerwear and blankets.

Depends on what you're putting it on. It does not always have to be tiny. I embroidered a design I made myself on a size 44 onesie - that's for late premature babies. It measures about 10 x 4 cm, some 4 x 1 3/4 ". But as you can see it consisted of two tiny flower designs and a swirl. Don't choose anything containing lots of stitches and you can get away with larger designs.

how big is the baby?LOL. no serious: I like personly a smal design that fits 4x4 hoop, because the clothes for the embroidery are also small.but if you want to embroidr something like blanket or dresspillow it can be larger of course. most inportnat the design has to be in proportion. good luck!

I like your other question better :)