One question per day, please. I'll answer the middle one.
The motif (recurring mini-theme) of the scarcity of goods is based on the real wartime efforts of the British government (and U.S., U.S.S.R., and Nazi gov'ts) to both conserve and profit from consumers. Remember, this is satire: Orwell is both imitating and exaggerating what he saw happening during World War II.
Price readjustment is a form of propaganda that enables the government and manufacturers to both limit the distribution and control the pricing of necessities (butter) and luxuries (chocolate). It's supply and demand, and the war has made supply so low and demand so high that the prices will, inevitably, become inflated.
The specific prices or types of goods don't matter as much as what the act and process stands for: it is a means of information control. Whatever the government says is a conscious lie. The Party lies about the prices; it lies about the scarcity; it lies about who they're at war with. It's a means of keeping the Outer Party and Proles hungry, tired, and stupid. It's a disinformation campaign against its own people as a means of control and profiteering.
A motif is a recurring image, sound, or idea that has symbolic significance and relates to the development of the overall theme. Throughout the novel, the citizens of Oceania struggle to obtain certain items like razor blades, chocolate, and butter. The Party controls the production and distribution of these everyday items and continually reduces the amount of each item every so often.
As was mentioned in the previous post, Orwell uses this motif to satirize the demand for such ubiquitous items during times of war. Unfortunately, Oceania is engaged in an unending war, and these common items become extremely rare. The Party also uses scarcity as a form of propaganda to manipulate and control the masses. One of the goals of the Party is to eradicate joy and comfort. They prefer to have the populace on edge, insecure, and hysterical. Not having the opportunity to groom oneself properly or enjoy a sweet treat is a simple yet significant way to agitate and control the population. Big Brother also confuses the masses by continually flooding the news with bogus statistics concerning various products. There is no way for citizens to know if the demand for an item they desire is justifiable. Regulating the production and distribution of everyday items is simply another way for the Party to impress its will upon the masses and reminds the reader that Oceania is truly a dystopian society.