Welcome, and congrats on your upcoming birthday trip! You will have an excellent time!
Staying off property you are at a slight disadvantage for booking ADRs (Advanced Dining Reservations). ADRs can be booked 180 days in advance of the day you are calling from. Resort guests can book them for 10 days beyond (so up to 190 days) the 180 day mark from the start of their stay. Meaning 180 days before their stay, they can call in, and make reservations for the 1st day of their stay, through the 10th day. Non-resort guests can book for just that 1 day, and must call back tomorrow for the 2nd day, and so on.
That being said, it is entirely possible (and to be honest, probable) that you won't be able to book Be Our Guest for lunch or dinner. Because people have a 9 day head start on you, and it books up. For example, when I booked my Be Our Guest reservation, the first 5 days (so 185 days from the time of me calling) were completely booked before I even had a chance. This was for non-peak time in Mid-November. So, in that regard, I wish you the best of luck.
If it's that critical to you, perhaps consider booking on-property (there are other perks that go along with being a resort guest as well)
Dinner with Fireworks at the Contemporary, is going to be at California Grill. This is a signature restaurant and it's price reflects as such - it's also an amazing restaurant with really great chefs and a solid menu. If you don't get a window seat there is a balcony guests can access during the fireworks show. Again, ADRs for this time fill up quickly (though not AS quickly as BoG) so be sure to call in or be online as soon as it is possible to book 180 days before.
Another alternative - if to view the fireworks from the Polynesian Resort, which can be done at 'Ohana - one of my personal favorite restaurants! No balcony here though, so a window seat is preferred.
DiveQuest at EPCOT requires SCUBA certification, and you must be able to present your C-card. They do this daily at 4:30 and 5:30pm - and it lasts 3 hours (40 minute dive-time). I'm not sure how early out you can book that, but you should call (407) 560-5590 to find out. If you don't hold a SCUBA cert, you can also do the EPCOT Seas Aqua Tour, which is a snorkeling experience.
Not too familiar with the parasailing, again call reservations for more details as to when you can book.
The Haunted Mansion should be open during your trip, so enjoy!
I've only ever seen Scrooge McDuck at the Very Merry Christmas Party, which, as you may have guessed, does not occur in March. Sorry. But you will have an amazing time without Uncle Scrooge!
