When I use the library import, which is now quite infrequently, I find it best to sort as I import, which does slow import time--but oftentimes the alpha tags make no sense if you don't do it this way.
If you import into the undefined or a temporary scanlist, you can sort the frequencies by scanlist in either the conventional frequencies tab or the trunked system talkgroup details tab. That way you can make sure you have everything assigned properly.
However, I don't recommend spending all that much time on organization until you do some listening. Leave trunked systems all in one scanlist, conventional frequencies loosely grouped, etc. After listening for a few weeks or so, you will have a better idea of how you want them organized, based on what is active and how it is used. If you start prematurely, you might spend a lot of time on a complex setup that isn't exactly what you will end up wanting a little while down the line.
I strongly encourage sorting as much as possible on a spreadsheet, as mentioned above.
If you do a search here (
Digital Frequency Quick Import), the results page has info about how to import conventional objects. Talkgroups are pretty much the same.