The prep jobs must be completed along with the other jobs in order to master each level of the tier. Otherwise, it is only necessary to complete them as the items are needed. You will need to return to the wiretap job for more wiretaps many more times than it takes to master the job.
You can only have a maximum of 501 and many people have that.
Cuba is different from Moscow.. No episodes in here.. It's the same with New York, 6 areas, then you have to master it to level 3.
joining a clan or family, or by posting to one of the many different sites that are mafia wars add sites. Depending on where you play, you can just type mafia wars into the search site, and many different things should come up.
so far there is no limit on how many family you can have on your mafia family but you can only take 500 mafia families to attack.
3
you need about 380+ illegal transactions. (this may be how many one needs total for all of the jobs requiring "illegal transaction records," but is an incorrect answer for how many are needed for just the three boss tiers - boss/skilled boss/master boss.)
320
As high as you can practically go
As of now, there is no known limit.
You should have as many of each item as you have mafia members. This way when they help you out in fights or doing jobs they are guaranteed to have the best items for their level. So if you have 100 mafia members, you should ideally have 100 of each item.
Loot drops are random in Mafia wars, to get them all it is suggested you do the "mugging job" in the New York level 1 tier over and over. This increases your chance of getting it because you are doing many jobs. If you only get about 7/8 items, you can always purchase Halloween crates at the Godfather's.