Sounds like a good plan, Abby. I don't know of any Macaw specific books that would have enough good info, other than broad based stuff, worth buying. I think you will find more specific info on the web. I do have some good books at home about behavior and training that aren't species specific, but are a good read. I'll find the titles and tell ya.
As for who to bring home first... that's a toughie. They will both be very needy, very demanding birds. The green wing will be bigger, potentially noisier, and more destructive (again, potentially. some aren't big chewers, tho most are, and greys can be very destructive too). The biggest expense difference with a GW vs a CAG is going to be the toy and cage size. The GW is going to need bigger toys (large bird size), which will be more expensive whereas the CAG will need slightly smaller (med size) but can still use the larger toys, depending on the cage size, so you can share/rotate toys between the two when you have both. Their dietary needs will be similar; both need a high protein diet and can eat the same food size/brand, so you're even there.
As for behavior, I recommend CAG's later in life if you plan on having kids, simply because they have the potential to mimic everything
including a crying and screaming baby/toddler. The GW can do so as well, but are nowhere near as good of talkers/mimicers. Both have the tendency to bond strongly with one person, so both will be jealous of any boyfriend/husband/children you add to your family later in life
The GW does have a bigger and stronger beak, so could hurt someone more in a way, but the CAG can do some nasty damage as well. The GW bite is more crushing and pinching, whereas the CAG is more cutting and tearing. The GW could break little fingers, the CAG could tear the skin up. Either way, you'll have to be very careful.
Ultimately, my advice is this. Which one do you want the most?
You may find you're unable to afford/have both or it will take a long time to do so. A GW will be bigger and harder for a new person to handle, they are intimidating in their size. But... a grey is probably just as intimidating to someone unused to parrots. Each has it's advantages and disadvantages, each has potential problems in your future, and they're pretty much even. The biggest differences I see is an larger maintenance cost on the GW for toys, bigger initial cost for the GW (cage primarily, depending on where you live the bird itself may be more expensive), and then the mimicry issue with kids and the CAG. Personally, I would go with the GW first because I know I would go absolutely insane listening to a CAG mimicking a crying baby for 50+ years lmao.
Hope that helps some!