Will I lose all my past data once we're in 2018? I'm asking since most of my queries are set with a date range of "last year and this year to date" or "this year to date" ?
If so, do you guys any best practice on how to manage that?
This depends on your date range setup.
If your setting is "last year and this year to date" you will have 2017 + 2018 once we are in the new year.
And for "this year to date" you'll only get the data for the current year, in other words 2018 once the year has changed.
If you wish to keep the old data in your report, you can either set the starting date manually, or use the "Combine new data with old" in the sidebar Options panel.