Hi Adspin,
I have started to play the keyboard by myself when I was around 28 years old.
The very first thing to start with was to learn the rules that build the music scales,
what is a tone, what is a semitone and where are those things on the keybed.
A melody(right hand) is written in notes of a scale so they are not just accidental notes.
Remember that notes have different durations.
Chords (left hand) are also parts of a scale and played accordingly to the melody notes and they are not accidental chords.
And then there is the rhythm.
Two basic rhythms: 4/4 rhythm like “Black Magic Woman” and ¾ rhythm like “The Blue Danube waltz”.
As for the tempo, everybody who never played music already knows that is the speed.
So up and down the C major Scale so your fingers will be familiar with it and your ears recognize how a major scale sounds.
Up an down the C natural minor scale for the same reasons
Then, up and down the C melodic minor scale.
Then continue with some more scales that begin with a white key.
Learn just the basics of music theory.
Not so much need to do all the practice exercises for your fingers unless you want to grow up and play Rachmaninof in a piano concert.
Practice with easy tunes at first with one finger as already have been said.
No need to read music if you cannot or try to find out by yourself what notes to press to play a melody.
You can watch tutorial covers for songs on Youtube or downlad thousand of free midi files and just play the notes they are playing.
There are programs like synthesia that they show you what notes to play.
https://www.youtube.com/watch?v=40TY2einWfQYour keyboard also can play midi files but unfortunately it displays them only in sheet music.
Only entry models of Yamaha show also the keys to the keyboards screen.
Just remember for the same song there are dozens of different versions in sheet music,midi files, live playing etc.
Find the easy one.
A teacher, even if he is the worst teacher in the world, he will save you time.