Congratulations on your purchase! You will enjoy running with Stryd.
PowerCenter is the best place to record and analyze your run data. You can link your Garmin Connect and Movescount account with PowerCenter. This allows your watch data to flow to PowerCenter, and you will have access to all your data.
At this time, old data in Garmin Connect and Movescount is not imported into PowerCenter. Only new runs will show up PowerCenter. You can also not import old data using a FIT file, as FIT files without power data are not accepted by PowerCenter.