Hi Stephen,
So was I. I don't have as many photos as you but I have my entire kids life in there and many many photos that I lovingly and painstakingly edited that I would die if I lost. But I am so happy with Lightroom that I have all but removed it from my system. I don't use it at all. I highly recommend it. Everything is in there that Aperture had from brushes to expert tools to complete photo management and I had zero issues moving a 1TB library. There are some tricks though before moving which I'd be happy to explain but they can be found on youtube in many of the migration videos.
Photos is unfortunately just not there. It is nicely organized but for people who
1) want a large library and must reference their photos I don't think it is built for that. Its simply designed for your every day point and shoot photographer who doesn't care to do much other than say I like/I don't like and have them organized nicely and some very basic edits. If thats ok for you and you can wait 3 years for some enhancements then great! But it will NEVER be a replacement for Aperture.
2) its not got any where near the editing tools that Aperture or LR has. Its extremely poor and Apple have just gone with the masses and kept it simple. I'm sure in years it will turn into a mess like iTunes but for now don't expect Apple to add your enhancement requests. They typically add what they want and expect you to use.
Lightroom caters for the amateur or pro photographer who wants excellent management and editing functionality. Do the following
1) Create full size previews for your entire Aperture library. This takes a long time!
2) refine and clean up your key words in Aperture
3) make 3 complete backups of the Aperture data base and original photos (or the consolidated library data base if thats how you did it) and store them in different places, this takes even longer!
4) run a complete migration test and expect it to fail, then you wont be disappointed when it works. A 1TB library took me all day to migrate but at least 24hrs to backup so expect to take some time doing this.
5) sign up to fstoppers.com and buy some of their basic and advanced Lightroom training tutorials.
Then be less worried that you'll lose access to Aperture with a future OSX update. Be happier with the editing and photo management tools in LR and dont be concerned that you have to use that lame app Photos.