I don't think that memorising piano music is that much different from memorising guitar music, but I was particularly intrigued by the author's (Francois L. Richard) claim that it is possible to improve your playing as well as memorisation by "practicing" pieces away from the keyboard, and whether anyone here has ever tried such a "practice method".
Strangely, I never found hand-independence to be a problem with the guitar, probably since the two hands have completely different jobs to do, but I was staggered to find that a seemingly simple thing on a piano like playing staccato with one hand and legato with the other, or forte with one hand and piano with the other, seemed much tougher than anything I had tackled on a guitar. Bartok has some wonderful exercises on both of these in Mikrokosmos book 2 
The kinesthetic feedback of intended finger position versus actual finger position is corrected in actual piano practice, by the detection of the ear of wrong notes. I'm pretty sure "mental practice" has no such feedback mechanism for incorrect movements. This is particularly important at my age, 64, because intended versus actual muscle movement is so variable in the aged. That is why they have senior PGA golf tournements, IMHO, because senior muscle movements change from day to day in a way that muscles in their prime, do not. I'm having to keep my hands in peripheral vision for multi-note jumps, for visual feedback. This is something I never had to do when I was 8-16; I was able to play accurately then with my head turned away from the piano.
Your exercises of staccato one hand, legato one hand, or forte one hand piano other hand, are interesting exercises, but IMHO are way too advanced for a first year student. Certainly nothing like that was attempted in the John Schaum method I learned from. Perhaps this is why millions of middle Americans learned piano from copyrighted John Schaum, instead of the public domain Bartok method. We certainly used public domain Schmitt and Czerny exercise books where appropriate.
The old-time practice of the teacher in hearing the student, and pointing out the differences between the student's performance and the desired one, is slightly obsolete in the age of the internet. Other than the lessons in copyrighted method books, you can hear nearly any track on an internet download, and aurally compare your performance to the "standard".
I'm not sure where you live, but my Mother found me a competent teacher by asking around the PTA meetings at the grade school. (parent teacher association). Another method is attending services various churches, and asking the pianist that sounds competent, who they recommend. The latter is more likely to yield a teacher with communications skill lack or emotional problems, than the former, however. The last method, taking from the piano store "pro", is fairly obsolete, as piano stores no longer exist. The APG, american piano guild, operates in the USA most places, but they do not sort by communication skills, only by degree attained. The teachers with the highest degree do not always have the best teaching skills, to go by some horror stories from conservatories and colleges I have heard.
Electric keyboard has the same spacing as a wood piano, but not the same force requirements and dynamic response. Also, 88 keys is rather rare with electric devices, as is the proper sit down position. Electrics are mostly played standing up, which is great for an audience, but not for turning pages through a book on the stand. So leaving out the youth who offered to teach you may have been for the best.
Good luck in your quest. I really enjoy re-focusing on piano in my retirement, and taking up electric organ as an additional skill made possiblt by the recent collapse in the price of old organs (needing restoration). Piano has the advantage that there is a vast repretoire of pieces meant for entertainment at home alone, before radio, television, and the internet took over that task with less skill required by the recipient. For example, I do several Scott Joplin pieces for strength training daily as well as routine entertainment, besides my mountain peak art pieces.