The Federation economy is not Communism - it is post-scarcity, as practically everything ultimately comes from almost infinitely abundant energy.
Communism is an attempt to share finite resources equally. Socialism is an attempt to ensure a minimum share of finite resources. Either way, there is an attempt to give even the lowliest manual labourers the same status and reward of higher professionals. Also, Communism is not simply an economy - it is an ideal: the removal of any kind of elite (ironically, all nations attempting Communism ended up creating a new elite).
The Federation has almost infinite resource.
Additionally, we do see most of the Federation through the lens of Starfleet, and it would make sense for the needs of Starfleet personnel to be met by the organisation to the extent that there is nothing wanting.
I do think you should ask those four questions separately, but here's some quick answers to think over:
Probably about the time the Federation actually formed (22nd Century). For one thing, older races like the Vulcans would have probably had post-scarcity economies already (logically).
It's probably more likely that they would have already reached post-scarcity before joining (there's usually some other caveats like the whole planet must agree to joining).
Probably the whole Federation (especially looking at life on Earth)
Well, in the west we're "indoctrinated" now to work hard and that sitting in an expensive house on a block of land with a pile of money in the bank is how we measure ourselves against others. In the Federation, people are educated to meet "the challenge and driving force then were to self-improvement, self-enrichment and the betterment of all humanity" - so, in the Federation, your value is based on how much better the world is with you around. You're not going to completely eliminate coasters, but the social pressure to be useful could be augmented by providing a minimum subsistence and then providing more access to replicators as a reward for societal contribution.