Firstly something thats classic is timeless. Think of any album, movie, car, wine, anything you consider classic.
Bringing it back to music, the album must be filled with pure dopeness in every single track. Not one or two hot, radio-ready tracks and 32 filler songs so the project can be called an 'album.' A music album should be treated like a photo album, only the best pictures make it in the photo album, so only the best songs should go in your music album.
IMHO an album should be condensed, these days everything is all about over-sized portions. Restaurants with too many menu items, too many crappy TV shows, vehicles bigger than your drive-way and/or garage, the list goes on. Do something more condensed that last in the ballpark of 1 hour and you songs will be memorable to the point that people will remember the track number of every song.
I'm sure there is more I can say on this, but honestly I don't think it's something that should be overthinked. Just do two handfuls (gripping handfuls, not barely holding on handfuls) of tracks that make you go "Yea! THAT is Hot!"
Another thing tho, don't be afraid of features lol