Indexing and querying jsonb nested arrays using Postgres 9.4 - arrays

Question

I'm currently using postgres (version 9.4.4) to save entire json documents of projects in one table like this (simplified):
CREATE TABLE projects (
id numeric(19,0) NOT NULL,
project bson NOT NULL )
The project json is something like this (OVERLY-simplified):
{
"projectData": {
"guid":"project_guid",
"name":"project_name"
},
"types": [
{
"class":"window",
"provider":"glassland"
"elements":[
{
"name":"example_name",
"location":"2nd floor",
"guid":"1a",
},
{
"name":"example_name",
"location":"3rd floor",
"guid":"2a",
}
]
},
{
"class":"door",
"provider":"woodland"
"elements":[
{
"name":"example_name",
"location":"1st floor",
"guid":"3a",
},
{
"name":"example_name",
"location":"2nd floor",
"guid":"4a",
}
]
}
]
}
I've been reading documentation on operators ->, ->>, #>, #> and so on. I did some tests and successful selects. But I can't manage to index properly, specially nested arrays (types and elements).
Those are some example selects I would like to learn how to optimize (there are plenty like this):
select distinct types->'class' as class, types->'provider' as type
from projects, jsonb_array_elements(project#>'{types}') types;
select types->>'class' as class,
types->>'provider' as provider,
elems->>'name' as name,
elems->>'location' as location,
elems->>'guid' as guid,
from projects, jsonb_array_elements(project#>'{types}') types, jsonb_array_elements(types#>'{elements}') elems
where types->>'class' like 'some_text%' and elems->'guid' <> '""';
Also I have this index:
CREATE INDEX idx_gin ON projects USING GIN (project jsonb_ops);
Both of those selects work, but they don't use te #> operator or any operator that can use the GIN index. I can't create a index btree ( create index idx_btree on tcq.json_test using btree ((obra->>'types')); ) because the size of the value exceeds the limit (for the real json). Also I can't ( or I don't know how to ) create an index for, let's say, guids of elements ( create index idx_btree2 on tcq.json_test using btree((obra->>'types'->>'elements'->>'guid')); ). This produces a syntax error.
I been trying to translate queries to something using #> but things like this:
select count(*)
from projects, jsonb_array_elements(project#>'{types}') types
where types->>'class' = 'window';
select count(*)
from projects
where obra #> '{"types":[{"class":"window"}]}';
produce a different output.
Is there a way to properly index the nested arrays of that json? or to properly select taking advantage of the GIN index?