Hi,
I just want to add a few thoughts...
Since the baby will be 6 months old, she won't exactly be a newborn, and you won't exactly be a "new" Mom, but... since you are a first-time Mom and are traveling with a large group, you might still be receiving advice from well-meaning relatives... "She needs a sweater on. She's too hot in that sun bonnet. A little ice cream won't hurt her," etc. Trust your own instincts, you (will) know what's best for your own baby. If you have this "type" of family member traveling with you, you may need to be polite but firm.
Are you flying or driving? Are you staying on-site at a Disney resort?
I recommend taking both a stroller and a carrier. You will definitely want your own stroller with you. Light weight is best if you'll be using the buses, and you'll want one that reclines. I like the Bjorn, you need to try them on and see what's comfortable for you.
Will you be nursing or still nursing? You may want a little "baby cooler" with dry ice packs, if you'll be taking bottles into the parks.
Because of her age, you'll want to speak with her pediatrician about which sunscreen to use. (Protect her skin, and watch out for the top of her feet, too.) I would have a sun bonnet on her, protects her scalp and keeps the glare out of her eyes.
As for bath time, you'll want her own baby products with you but also... I hated sitting my children in hotel tubs. Bring your own disinfectant from home, I travel with my own can of Dow Bathroom clearner and a can of Lysol. (You don't need to scrub the tub, but spray it completely and then rinse with the shower head.) Bring something to sit on in the tub, so you don't have to use the germy rubber mat.
Also, throw a container of the pop-up disinfectant wipes in your diaper bag and use them to wipe down high-chair trays or dropped toys.
You'll need all the basic items with you... infant tylenol, blankets, butt cream, etc. After she's here and as the trip gets closer, you'll know more of what she needs to keep her comfortable and happy... lots of bibs if she drooling, teething gel, favorite toys and teethers. etc.
I have 5 children and all of them have been great little travelers.