
There should be a drop down menu at the top of the Finder winder that allows you to Group all your files by various criteria. One of them is Tags. Color tags will separate out the clips you assign per color and you can easily select all the clips from a particular keyword and drag them into FCPX (icon or list view). When you drag your clips into FCPX, it appears that the applied Tags will be automatically created as a Keyword Collection in the Event the clips are dragged into. Turns out you don't need to create them in FCPX in advance! However, if you can actually separate out the tagged clips from the Finder before importing, you don't really need the keywords in FCPX — so you can delete all the keyword collections that aren't needed (and this will not delete the imported clips - they'll still all be in the Event they are imported to.) Useful if you don't care for the extra "clutter".
Once all your clips are imported into FCPX, in any Event (pun intended) the sort order can be set to Content Created. You can also simply Group clips by Content Created and FCPX will organize them by labelled Dates. [I don't care for this feature and usually have it turned off.]
I've never been able to see any advantage of using the FCPX import "function" over direct interaction with the Finder. For me, it actually takes considerably less time than going through Import. I will grant you that the option to sort clips by Tag in the Import dialog might be something to consider. It would also be convenient to be able to use that metadata in the Inspector. Tags ARE automatically applied upon Sharing a video (and can be viewed in the Info pane of the export dialog). Tags are available in the Timeline Index. It is "unusual" for Apple to leave this metadata kind of separated from the rest of the really huge amount of metadata that's available. I can create an Effect that will automatically create a Title with a Clip's Notes. It would be useful to be able to do the same with the Tags.
As for importing 300 clips — it would only amount to about a few MB of text (xml) data regardless of how long the actual video is (no clips are actually, literally imported into FCPX). I have always recommended that you set up FCPX to leave all original files "In Place" (and on a separate disk) unless you have to share the library with other editors. With this setup, it wouldn't slow you down to import all your clips at once. Once tagged (color coded) in Finder, select all and drag/drop them all in an Event (not the storyline — that's a whole other thing), FCPX can take care of the rest... except for setting the sort order, if needed.