Some layman answers to your questions:

1) It is possible, but probably unlikely, UNLESS LE has reason to suspect that you are involved in other criminal activity.

2) The limits of a search warrant are set by the judge who issues it.  If a warrant is issued for the premises at 123 XYZ St, everything there is fair game.

3) If you are not prosecuted, or are exonerated any money or property seized should be returned.  Unfortunately as a result of the federal RICO (organized crime) laws, this has changed.  To combat the maffia, the feds have allowed local authorities to attack property.  If you are a suspect, and you can't prove that the car you are driving, the house you live in, your cash on hand, etc, isn't  the proceed of criminal activity, it can be permanently seized.  There have been more than a few local PDs and sheriff's offices that have abused this.

1.) If a low-key provider got arrested, law enforcement would perform a search incident to arrest. The vicinity around the arrestee can be searched. This includes any envelopes, purses, bags, etc. within arms' reach. If in a car or nearby a car, the car would get searched. Police have a lot of leeway in warrantless searches because of the time and effort it takes to get a search warrant. Thus, many searches are conducted without a search warrant. Search warrants are usually for investigations in which there is no immediate arrest.

2.) The Fourth Amendment says "no warrants shall issue, but probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." So search warrants have to state the location to be searched, but that can be very broad since entire buildings can be named. Search warrants also have to state for what items are being searched. However, that too can be very broad. For example, a search warrant could be issued for drugs and since drugs can be hidden away in lots of places, this gives the police wide discretion as where to look. Police also aren't supposed to shut their eyes and ignore what is in plain view.

3.) Not necessarily. Police might keep seized property as relevant evidence or something that merits further investigation. If it's the proceeds of illegal activity, police can keep it too. An attorney may have to file a motion to return property.

I doubt the police would take the time to get a warrant unless they had reason to believe you had narcotics or some other fruits of a crime in you home.  They would have to articulate in the warrant why they felt you had the items they wanted to search for in your home and convince a judge to sign the warrant.

The search warrant must include probable cause to conduct the search in the first place and the items that the police are looking for must be identified in the warrant.  If the police are looking for stolen TV sets, then they can’t open dresser drawers pursuant to their search.  However, if they are looking for something like stolen jewelry and they open a dresser drawer and find narcotics then the seizure of the narcotics is legal.

Generally, any items seized pursuant to a search warrant that are not used as evidence and are not contraband are returned to the owner upon the owner’s request.

Like everything else, this is how the system is supposed to work but it is still subject to abuse.

1. They may want to follow up and search other locations that might have evidence of the crime.  For example, if a person was arrested at a hotel, they might want to search the person’s house.  (See below for the type of things they would be looking for.)  However, I would guess that the odds are unlikely, since they could probably make the case on the cops' testimony regarding the circumstances of the arrest.  It depends on how efficient they want to be and how much they want to spend in terms of recourses.  My guess is they would be going for a guilty plea, so they don’t need too much more, but it wouldn’t prohibit them from doing so.  More of a question of allocation of resources rather than legal limits.

2. They can search for anything that might be evidence of the crime as long as there is a reasonable basis to believe the evidence may be where they want to look.  The warrant can be pretty broad.  It doesn’t have to be very specific.  For example, if they know a gang member lives at a certain location and have arrested him, the warrant may say “any papers or other evidence showing that X inhabits or frequents a particular location.  Any photographs, drawings, or writings reflecting membership or association with other gang members.”  (That is off the top of my head, so it isn’t exact.  But that is the type of thing that they can look for.)

When they suspect that crimes have occurred using a computer, like maybe posting on a site known for being a conduit for illegal activity, they can seize the computer and examine the hard drive.  There could be a trial of messages that would be evidence of the crime. “Hello. Would like to meet. How much?”  And so on.  Needless to say, 300 daffodils isn’t exactly subtle unless you also work out of a flower shop.

3.  Unless they get a conviction, they should return anything.  However, there are civil forfeiture statutes that allow them to take fruits of a crime via a civil proceeding without a criminal conviction.  I am not sure of the details, but that would also have to result in a legal proceeding before they could keep it.