PowerBi online limits using Google Analytics?

Hi agarcia,
I understand your questions as I have tried to figure out the same thing some time ago.

- PowerBI Online does not allow queries from the Google Analytics API (only PowerBI Desktop)?
You can only use the pre-built data source to connect to your data. Querying the GA-API with custom queries is not (yet?) supported in PowerBI Service. You can do some workarounds using Post Requests and functions in PBI desktop, but I found it not feasible.

- What is the maximum number of rows that displays a table of the dashboard?
PowerBI does not seem to have a limit that would be applicable to one query of GA data. But you have to distinguish between the data table that lies behind your dashboards and a table you would actually want to display. Displaying >10k rows to the dashboard consumer make no sense at all. 
The GA API does have a limit of 10,000 result rows per API query. If your GA query exceeds the 10k row, it seems that PowerBI does make the extra queries to retrieve all rows. I have just made a test and my countrows(datatable) measure returns 165k rows of data. So your data should be "complete", if I understand your worries correctly.

- Is possible to use sort and filters for the Analytics API queries?.
Unofrtunately, no.
To everyone else: The GA API allows you to specify filters, segments and sort orders that will alter the result of your GA Query even before it arrives in PowerBI. This is not supported by the PowerBI service.

My suggestion to you (easy setup):
- Use Google App Script to insert your query data into a Google Drive spreadsheet.
- Make the script to get only new rows of data and add it to the sheet.

- Then use PowerBI to connect to that spreadsheet as a data source.

My second suggestion to you (more advanced setup):
- Build an application that uses a serverside language to query your data
- Store the results in a database

- Then use PowerBI to connect to that database.

Unfortunately I do not see a better way at the moment.