These past few months I've been teaching myself how to play piano, using my background in guitar and a basic knowledge of music theory I've picked up from that. I am having difficulty "memorizing" seventh chords and inversions. I know how to formulate any type of chord technically, but I want to be able to play chords quickly and not need to figure out each note. 

To be more specific, I'll list what I already know and try to explain the next step I want to take. I'd greatly appreciate any tips on how to achieve that next step, or what intermediate steps I'm missing. 

On piano, I'm already comfortable 'quickly' playing:

* the 12 major scales starting at the root
* the 12 major chords in root position
* And of course, flatting my middle finger (the third) to play the 12 minor chords

By quickly, I mean my hands can somewhat instinctively find whatever I'm looking for. If I want to play a B major, I don't have to think about what's the major third and what's the perfect fifth from B, I just know what shape to make. I'm having trouble extending this to seventh chords. If I'm playing a seventh using my left hand, I currently make the shape using my pinky (root), middle (third), and thumb (fifth), then move my thumb to the (major or minor) seventh, and awkwardly shift my ring and index fingers to the notes I was holding with my middle and thumb fingers previously. That's obviously untenable. The two methods I'm aware of for memorizing chords are either to memorize the four-finger shapes (which seems a bit scary but perhaps I should knuckle down and try to do it) or use chord stacking, where for instance to play a major seventh, I'd play the root and then play a minor chord based off of the third. This seems like a "lot" to think about while playing however, and so I'm concerned this isn't the right way to approach 'memorizing' chords to be able to play them quickly. Is there another method or should I just try one of these two (or both) and slowly keep practicing?

Anyone have a practice regimen they prefer? Just learn a few sevenths at a time? How could I introduce memorizing inversions, ninth chords, augmented chords, etc into this? In short, my brain knows what it wants to play but my hands are too clumsy to move my fingers around quickly, and without the comfort of movable chord shapes that I've been spoiled by on the guitar, I've found myself at an impasse for continuing to teach myself piano. Thanks (and sorry for the verbosity).