MongoDB Storing User Files - mongodb

Question

I've been trying to become familiar with using MongoDB, particularly GridFS (which is implemented through the client). In a project I'm playing around with, I have users with corresponding locations, followed by corresponding data, but it is currently just stored on a filesystem which will ultimately lead to problems.
So an example data structure I have now is:
./(userId)/images/img1.png
./(userId)/data/sensor1/sensorOutput1.data
./(userId)/data/sensor1/sensorOutput2.data
./(userId)/data/sensor2/sensorOutput1.data
./(userId)/data/sensor2/sensorOutput2.data
So, in looking at GridFS, I see that you can pass attribute/values to be associated with the meta-data for each file. Looking at this setup and after reading tutorials on MongoDB, I thought of this approach:
Have one database with multiple collections (such as data or images just to separate some of the data). Then in each of the collections, have attributes for each document such as:
Under image collection:
{
"userId": 5,
"path": "",
"filename":"img1.png"
...
}
or
Under data collection:
{
"userId": 5,
"path": "sensor1",
"filename": "sensorOutput1.data"
...
}
Alternatively, I could just have a collection, and for the sake of this example, I'll call "Everything"
{
"userId": 5,
"path": "images/",
"filename": "img1.png"
...
}
{
"userId": 5,
"path": "data/sensor1/",
"filename": "sensorOutput1.data"
...
}
{
"userId": 5,
"path": "data/sensor2/",
"filename": "sensorOutput1.data"
...
}
Do either of these solutions seem reasonable? Would I then create an index on the "path" attribute? I've seen examples for adding files to MongoDB just haven't found one with how to structure user files.
Thanks!