bigger speaker holes to let more volume through and shorter vol/power key height to reduce mis-click (and rattling?)
but frankly, I don't find any problem with the original one that I have
whoever can get it at a nice price should just get it, IMO

it's your IMEI no.
it's either starts with 310K or 311k
311K is the newer batch, if i am not mistaken

serial, right
it's on the bottom of your box

no

Wow, you manage to leave your phone on standby for 3 days? So boleh tahan, I can't put in down for longer than 1 hour XD

f yeah!
About cases, spg ultra hybrid user here, I'm OK with the size and liking that you can customize the case by putting your own pictures under the transparent layer