#1
ok here I want to say something... i will give an example, bcause i cant explain it well...

this day I learn a new solo, (2nd solo of knocking on heavens door) I have completely play it well (on this first time learn)...
then at that night, when i try to play it back, seem like i have forgot many lick of the solo...
is this relate to any theory? or like something called 'muscle memory'...
#2
I would say just practice it more. Sometimes it takes a while for my fingers to get used to playing a certain song, so I just practice it as much as I can.
#4
yup its simple memorisation my friend, Would you be able to learn a poem after reading it once over? I doubt it and the same goes for music.
It doesnt matter how well you can play, you still have to remember what to play and when!