I'm an old
Disneyland vet who's been planning our first WDW trip, which is next week! You can check out my plan thread where I talk about my struggles planning our first trip, but I'll answer a few based on what I've gone through.
You need to be ready for the reality that booking advanced dining reservations (ADR's) for popular spots is harder if staying offsite. Not sure if you know, but when staying at an official disney resort (or swan and dolphin too I believe) you get to book not only at 60 days, but for every day past 60 days you will be staying up to 10 extra days. So if you have a 10 day stay at Art of Animation, you can book "60+10", or up to 70 days out. Which means resort guests can completely book up a restaurant before off-site guests even get a chance.
We are staying offsite, and we eventually got everything we wanted... but we started 83 days ago, and I just got the last ADR I've been trying for today. There are TONS of great places to eat, but getting a reservation for many of them could be extremely difficult. Cinderella's Royal Table, Space 220 (and Space 220 Lounge), Topolino's breakfast, Artist Point Story Book Dining are all EXTREMELY tough to get if staying off-site. None of these had any availability for me when I booked 60 days out (we only got them later). And almost all character dining is pretty tough to get good times for at 60 days when staying off-site. While not as tough, getting an ADR at Be Our Guest or Chef Mickey's or even Sci-Fi can still be challenging! Where you want to eat is kind of up to your group, but we knew we wanted to do as many character dining experiences for our first trip. If that's you too, then you'll need to be flexible in your times because chances are, there won't be many openings at even 60 days for these. If you're not picky then there are plenty of places that have last minute reservations, but eating at Tony's when you really wanted to be at Be Our Guest probably isn't how you want to spend your first WDW trip. I'd suggest watching YouTube videos of WDW restaurant reviews and see what catches your eye! That said, ADR's aren't what makes or breaks a disney trip for many. And you might just be too busy to stop for a 2 hour meal during your park day. And don't forget, there are TONS of great food outside the parks. Disney Springs restaurants are easier to get a reservation for, and some even can be booked on OpenTable, avoiding the whole disney ADR mess.
As for magic bands, they aren't necessary but are convenient. Most phones can replace magic bands for a lot of things, but I hear that magic bands are best for capturing on-ride photos. We will probably be buying magic bands when we arrive, but we know we could do without them if we wanted to.