Had some free time and did a bit of 'testing' in Photos. I'll send you a bill later this month.
First, despite the info that says iPhoto runs in Sierra, I ended up using Photos instead. While iPhoto opens and displays my images, I could not get the standard Nav dialog to accept my (Cancel/Create/Save/etc.) button selections where I tried to create a folder for the images I had selected to Export. Not sure why. I even had to use "Force Quit" to get out of iPhoto! Simply opening Photos will automatically import your iPhoto library/images without affecting their state.
It appears that you might be able to maintain your 'event' system, at least with the 'date' structure in Photos. It will not be an "all-in-one-process" however.
The process is to simply Export a selection of images from Photos/iPhoto into a specifically name directory. In other words, select an 'event' in Photos/iPhoto and Export it. I'd suggest using the event's name for the new directory. Obviously, since you have thousands of images, this could take quite a while.
The default location that LR uses for Importing is the Pictures directory (a normally created directory in every users directory).
Note: You should probably look in the Pictures directory for a directory called "Lightroom". That should have been created when you did your previous importing. Inside, you should find a "Catalog.lrcat" file. That is the database that contains links to all your images and any meta data that may have been imported from iPhoto. I'd suggest simply archiving everything in that "Lightroom" directory so the new imports will be in the new directory rather than ending up with duplicate entries in that old database.
If you are looking for a "LR forum" I'd recommend
Lightroom Forums. I've not been there long, but they seem very helpful and friendly, even to noobies! Once you sign up, you can also download a LR Quickstart Guide. Here's an excerpt of a section on organizing images:
Importing photos into Lightroom doesn?t force you to rearrange them. If you already have a well thought outling system, you can keep your existing folder structure. As far as Lightroom?s concerned, your choice of folder structure doesn?t make a lot of difference. Folders are just a place to store the photos, and you can use metadata/keywords to organize them.
That said, you do need some level of organization to make it easy to back up your photos, and it?s best to avoid duplicating photos in multiple locations (other than as backups, of course). Many people choose a date-based folder structure, with folders for days (or shoots) within folders for months, which in turn are in folders for years.
And a warning about 'messing' with your images outside LR:
You can rename the files at any time, as long as you do it within Lightroom, but doing it at the time of import means that any backups you make while importing will have the same names as the working files.
(emphasis added)
Importing from Photos can be done, even if you have 14,000+ images!
Thread: Importing from iPhot[sic] and PhotoGood luck, young Will Robinson!