Requiring X number of levels before multiclassing destroys any traditional style multiclass characters. It also can result strange things. A paladin that falls at low level would no longer be able to advance; he can no longer advance in paladin, and doesn't have the level needed to enable multiclassing. A rogue who undergoes a sudden conversion can't become priest or paladin. If a crucial character in a group dies, other characters can't multiclass to fill the gap. Low level characters are about the same age as college freshmen, some older, some younger; how many college freshman end up changing their major? They don't need to finish their initial choice to do so.
Splitting first level into 4 other levels seems pretty odd. First level characters have little in the way of skills, offense, or survivability. About the only thing they do have are stat bonuses. From my experience in other RPGs, starting DnD characters are weaker than other starting characters, and I think it's somehwat crazy to weaken them further.
I'm not sure where Metheus's problems are coming from. Our group doesn't run around around looking for gold and then returning to town to buy items from the Magical Sears catalog. We haven't made a choice not to do so to preserve some kind of style. We have the resources to act in that manner quite efficiently - teleport, a helm of teleportation, and 2 characters with "Studied Carefully" or "very familar" locations in Waterdeep. We have jumped around, or at least had the wizard port, to buy some things. Things like scrolls of low level spells. Also, we've wanted to sell items that no one wanted to use. Buying items seems much less efficient than making them yourself anyway.
The Realms, at least in 2e, had tons of high level wizards, the same # of Chosen of Mystra, etc. At least now they've added higher level villains like the Shades so the "Forces of Good" shouldn't be stomping down on every because they out number and out level villains. Population counts probably changed because different counting methods. I don't have the books with me, but it seems likely that 2e books counted the population in the town proper, while 3e ones count the number of people living in the area.
Of course, in previous editions, if you wanted to roleplay a fighter as crafty and sneaky, you could. However, you weren't. Now you can both act sneaky and be sneaky because of cross class skills or multiclassing.