Oh, this is the kind of question I love to puzzle over! There are many ways to do it, but here's the itinerary I would suggest. My strategy was to have you get to most of your "long line" rides in the first hour or two after rope drop (doing the rest of the "long line" rides later, most with FP+), so you can relax and slow down for the rest of the day. I also built in a lengthy break in the middle of the day. I avoided relying on a fourth FP+ for anything, but it's a great tool for revisiting favorite attractions after your initial three are used up, if you have the inclination. You're visiting during a low-crowd time of year, so you may find that you don't need it.
At rope drop (head straight down Main Street toward the castle, stopping for a family photo if desired, and then to the right of the castle, into Fantasyland):
Peter Pan's Flight
Adventures of Winnie the Pooh
[Then, head through Liberty Square and into Frontierland for...]
Big Thunder Mountain (w/ child swap, assuming both adults want to ride)
Pirates of the Caribbean
Jungle Cruise
Magic Carpets of Aladdin
Swiss Family Treehouse
[Now it's time to stop at Aloha Isle for Dole Whips, and then head back through Adventureland, Frontierland and Liberty Square at a leisurely pace for any non-headliners you wanted to do and didn't -- perhaps the Enchanted Tiki Room, Country Bear Jamboree, WDW Railroad, or Hall of Presidents. If the line is still reasonable for the Haunted Mansion - e.g., 15 min. or less - do it now.]
[LUNCH/NAP BREAK until 4pm, or earlier if you intend to see the 3:00pm parade]
[On your return to the park, take a more leisurely stroll down Main Street and head to the right, into Tomorrowland:]
Buzz Lightyear Space Ranger Spin (with FP+)
Tomorrowland non-headliner of choice (Monsters, Inc. Laugh Floor, Peoplemover, Carousel of Progress)
[Now head into Fantasyland]
Under the Sea
Enchanted tales with Belle [with FP+]
Seven Dwarfs Mine Train [with FP+ - once that final FP+ is used, see if you want to try for a fourth for Dumbo, or to revisit a favorite attraction from the morning] (child swap)
Dumbo
Fantasyland non-headliners of choice (Barnstormer, Mickey's Philharmagic, Prince Charming's Regal Carrousel, Teacups, it's a small world)
Haunted Mansion (if not done before)
[Obviously you'll need to stop for dinner somewhere in the evening. Use the WDW Railroad (stops in Fantasyland/MainStreet/Frontierland) to save some steps if you need to cross or leave the park for dinner. Once you've completed everything you wanted, you can revisit favorites, if desired -- keep in mind that lines drop as the evening progresses, and you can get in line for an attraction right up until a few minutes before park closing and they'll let you on, even if you're not boarding until after closing time -- personally, I'd recommend another spin on Big Thunder Mountain at the end of the night. It's a totally different experience in the dark.]
As to your questions, I love touringplans but if you're only going to one day you can get some nice free ones from easy wdw dot com. No need to run down Main Street when you first get there (although I certainly recommend being at the gate well before rope drop -- once inside the park, a reasonable walking pace will get you where you need to go and allow you to take everything in.)
My top Fastpass+ recommendations are (in order of importance): Seven Dwarves Mine Train (long line that builds fast for a very short ride), Enchanted Tales with Belle (takes too long to waste "rope drop time" on), and any other headliner (if following the suggested plan above, Buzz or Dumbo -- otherwise, Big Thunder, Pirates, Jungle Cruise, Peter Pan, Pooh or Haunted Mansion) that you won't be able to reach in the first hour or two after rope drop.
Have fun!
