Couchdb, Mango queries and Indexes

I use Mango queries with Couchdb when users want to search the database. They can search by multiple fields in the document.

To simplify I have a document with three fields all of which can be searched to find the document.

FieldOne: cow
FieldTwo: pig
FieldThree: dog

When creating a mango index for the query what fields should I use? Should I create and index with multiple fields? Does the order matter?

There are also three different document types (A, B C) defined in a field. I only need to search one, is it possible to exclude the other types from the index to make it faster?

Field_Type: A

It would make sense to me to be able to run an index against a view to only search through the documents I am interested in. Is this possible?

Example indexes

One index on field known to appear in the query

  {
       "index": {
          "fields": [
             "FieldOne"
          ]
       },
       "name": "foo-json-index",
       "type": "json"
    }

Multiple indexes, not sure if used or not?

 {
       "index": {
          "fields": [
             "FieldOne",
             "FieldTwo",
             "FieldThree"
          ]
       },
       "name": "foo-json-index",
       "type": "json"
    }

Or multiple indexes to choose the correct one when building the query?

which is the correct approach to get the fastest search results?