Well, my *dream* is to get to a point where I can use a piano the way I use a guitar -- which is, frankly, as a very expensive karaoke machine. I know few-if-any classical pieces on guitar. I'm not a good soloist on guitar. But I can pick up a guitar and play out a nice-sounding chordal accompaniment that I can sing over. I'd love to be able to do that on piano (minus the 'picking up', of course), but I can't, and I begin to wonder if I ever will.
And the thing is, I have no idea how difficult it is to play simple pop music on piano. I know that the easiest thing in the world to do with a guitar is to strum chords and sing over them. Playing even simple classical pieces on guitar is orders of magnitude harder.
For all I know, it may go the other way on piano: playing a decent accompaniment on piano may be much more difficult than it sounds. (Among other things, it may require a stronger background in music theory and voice-leading than I've got.)
So, question for the hivemind: what should my plan of attack be? Should I find a local instructor to take lessons with? Would it make more sense to track down the appropriate drills, pick some songs to learn, and proceed on my own?
_____  Yes, yes, most kids get to that by about age five. Wasted youth....
Well, I'd agree with Judovitch for the most part - although "Bohemian Rhapsody" is a boatload more difficult than say, Chopin's "Prelude in C Minor". There are other examples, but that's irrelevant to your main question.
I think the biggest impediment in going from guitar to piano is the irregular layout of the keyboard. With the guitar one can learn a few basic "shapes" (i.e. an Emaj chord) than practice laying your index finger flat across the neck to barre while making that same shape with your remaining fingers. Move up and down the neck and voila - all the major chords are now at your disposal. One can also employ a capo as an artificial barre to make songs in odd (for guitar) keys playable with simpler fingerings.
No such luck with piano. While, obviously, the intervals remain the same - the way one's fingers lay on the keyboard look very different playing the same type of chord in different keys. This can be really frustrating for students.
Two option for you Peter:
1) Get a chord book (with pix or diagrams of piano voicings and inversions) and some sheet music of something you'd like to learn. Ignore the notation and read the guitar chords (not the tablature - just the names of the chords) and look them up as you go. It will be tedious at first but you will soon get to recognizing the chord names and associated voicings.
2) Find a teacher who will teach you songs you want to know and will walk you through some of what I described above. This option might be best and could be something done in a few lessons, at least enough to get you on your way. Said teacher could possibly introduce you to chart reading & writing - something you would find a lot handier for your goals than struggling with notation. Hell, I've been at this forever and I hardly ever get asked to read notation anymore except on the few occasions when I find myself in a classical setting. Charts in standard and Nashville formats (the latter simply using a combination of Roman and Arabic numerals so you can play it in any given key without having to transpose in your head) are the rule for most applications these days.
That said, I'd be happy to sit own with you sometime, see where you are and run you through some of the basics of what I've described. Hopefully at least give you a jumpstart.