If you are bent on not having a teacher in the formal sense, my advice is to dig deeply (and I mean deeply) into this forum, let something grab your curiousity, follow it for awhile, come back with specific thoughts and questions about what you find.Welcome .
So, to help us know where you're at in reading: do you know the musical alphabet? how sharps and flats work? Where to find middle C on the page and on the keyboard? What numbers represent what fingers?
And save up for a real piano! If you're concerned about bad habits, you'll pick up a lot of them on a digital piano.
I envy that you were able to find a decent piano for $50! When I was looking all I could find for cheap were old clunkers with uneven action, buzzing or even dead notes... But now that you mention it, it probably would've been cheaper for me to get one repaired than it was to buy new. Oh well...