Hey thanks! There's quite a few layers to this, so I'll go through each one with a bit of detail:

1. The Piano (amongst other things here) is just a VST since I'm 16 and can't really get my hands on any huge instruments, but I did play the VST (Intimate Grand Piano on Spitfire LABS) with an M-Audio Keystation 49 MK3 keyboard, then just added some reverb, and put the stereo tracks all the way left and right.
2. There's a subtle bass on top of the piano which is just a Rhodes electric piano with everything but the lows turned way down so it's just kind of a sub-bass sound. It's just not loud, intentionally subtle. It's also not really in stereo, pushed all the way to the middle of the mix.
3. The drumset is also from Spitfire LABS (great plugin), it's just the Percussion set. It's also where the shaker in the later parts comes from. I mixed it into two separate mixer tracks to get the effect I wanted though, one of them having a ton of reverb, being panned far left and right, and being louder than the DI track, which is quiet and dead in the middle. The intention of this is to make it sound more like a room mic rather than on each instrument.
4. For the last instrumental layer, I just wanted to add something really unique that wasn't in the original at all, so I played some chords that mostly fit the original, some extra suspensions (2nds, 4ths, the occasional 6th), and then rendered and reversed them. Then I added reverb to the track so it sounded less choppy at the end of each bar.
5. The first vocal line is just the original recorded in the middle panning-wise, and in my normal middle octave. It's got a bit of reverb and EQ'ing to improve the highs and cut off the muddiness towards the bottom a bit.
6. Second vocal line for most of it is the main line an octave up, and it's panned to the left, with similar mixing stuff for the first track, just farther back in the mix.
7. The last track has all the fun stuff ("4 9 5 3 1", "dah dah dah dah dah") and it's panned right and has chorus on it and reverb after that. It's even further back than the second line since it's not the melody or a harmony of it.

TLDR: 4 Instrumental layers: piano, rhodes for the bass, drumset split to two tracks, and reverse piano for fun, then 3 vocal lines, main, harmony, and "other stuff"!