Looks like a lovely sweater. You're going at knitting like gangbusters!!
A few thoughts... because you know I can't leave well enough alone
First.. what yarn are you using? The original yarn is a cotton blend that looks very drapey.. have you knit with cotton before? It is a completely different beast from knitting with wool. It doesn't have the same elasticity as wool which means you have to work harder to knit it.. and your hands will tire more easily. If you've not worked with cotton, I'd highly recommend knitting atleast a washcloth using a ball of cotton from walmart before you decide if you like knitting it enough to make a whole sweater out of cotton. Personally, you couldn't pay me enough to knit something that large out of a yarn that's mostly cotton, no matter how soft and drapey it was. I substitute a linen such as
Louet's Euroflax or a cotton/tencel blend with a fairly high percentage of tencel like
Classic Elite Premier (which I see has been discontinued. NOOOOO I wanted more!! This is why I stash!!) They're much easier on the hands to knit and I can stitch for a longer period of time with them without my hands starting to hurt.
Second... swatch, swatch, swatch! BIG swatch, and make sure you wash it and block it before measuring. Cotton/linen yarns change gauge fairly dramatically when they are blocked, and the larger the size of your garment the more it will be affected.
Third.. Sizing. You said you're having trouble deciding on a size. Does this sweater have any waist shaping? It sounds like you're rather busty but otherwise fairly small framed. I would do a bit of research on adding waist shaping and even some darts at the bust to make it fit better, otherwise you're going to end up with something that will fit you well in one place but either hang or be stretched too thin elsewhere. This is where having an accurate gauge swatch is important so you can do the math to get the sizing correct. A really good example of what adding bust darts and shaping can do for a sweater can be seen in the
Tomato Sweater. Take a look at that pic. It looks fairly shapeless and rather blah, doesn't it? Not at all flattering to the figure. And what busty woman would want that stripe calling attention to her widest part? Now look at
this version - it's the exact same pattern, but the knitter added some darts to accomodate the bust, and moved the stripe. Looks totally different, and SO much more flattering! In fact when I saw that version I knew I had to knit it too since I am shaped very similarly and that is so flattering I had to have one too and cast on the very same week for it!
Darts can sound complicated when you start researching them but they really aren't that hard - you just have to be willing to do lots of measuring and some basic arithmetic to get your numbers right. If you decide to do them and need some help figuring them out, feel free to come pick my brains about them!