What procedures or requirements police need to follow to obtain a search warrant?

You're asking a bunch of questions all wrapped up in one.

The law on informants in warrants can get a bit convoluted, but the first question is whether the informant is deemed as a "reliable" or an "untested" one by the police. In the warrant application, the police have to provide sufficient information to establish probable cause to search. If part of their affidavit is information supplied by an informant, they must disclose things that not only show the credibility of the informant, but also their bias (i.e. are they working off charges, are they getting paid for their information, etc.).

Does the information supplied by an informant need to be corroborated? Yes, to an extent, but it depends on the case. For example, if they sent an informant in to do a buy at a suspected drug house, the single transaction may be sufficient to establish probable cause that more drugs exist, leading to a warrant. If however, the informant merely says that there are drug sales going on at a particular location, the police would need to corroborate that information by watching the house, documenting traffic to the door, run criminal histories of the visitors to see if they are drug users, etc.

Regarding the identification procedures: Sorry, but I have to say "it depends" again. If the informant knows the suspect, then showing them a single picture may be for investigation purposes or identification for court proceedings. It's unusual where the informant doesn't know enough about the suspect where a group photo spread would be necessary.

As I said, the laws and cases surrounding search warrants, informants and sealed portions of the warrants go on and on. Every case is unique and if there is an informant, a motion should be filed to try and unseal the sealed portion to disclose the CI and/or challenge the warrant.