OP definitely has the right idea by doing it a little at a time. In the end, it will be easier for everyone to deal with. Trust me, you WANT to do this before it's too late. Don't leave it on your kids (or whoever else will handle things when you're gone.)

Call it downsizing, Swedish Death Cleaning, or purging - whatever you want to call it, you need to do it sooner, rather than later.

It took months of cleaning, donating and selling to eliminate all of my late parents' belongings after they passed. Everyone in the family got what they wanted of the sentimental items before we began the total cleanout. Mom had a lot of sentimental items. Dad was a flat-out hoarder, although a relatively orderly one. He had every single tax return he and Mom had filed for the entirety of their marriage, every single paystub from every paycheck he ever earned, every bill they ever paid, bundled together by month/year (over 50 years worth), every owner's manual for every item they purchased - every clock radio, lawnmower, toaster - all of it. All of that paper filled a massive 90-gallon trash tote at a community shred day. (Best $10 I ever spent to get that all shredded in a matter of seconds!)
The garage was a nightmare - 10 of every size and type of screwdriver, socket, wrench, saw blade, etc; 1000s of screws, bolts, nails, fasteners, hooks - you name it, he had it; dry-rotted plastic grocery bags full of neatly folded plastic grocery bags (100s of them); paper bags full of sawdust (??); a pile of wood scraps from projects that was over 6' tall and 5' long (we had lots of bonfires with that), old rotted floormats from cars they hadn't owned in decades, along with a couple of seats from the cars as well.

When it was all said and done, I swore I'd never, ever do this to my own kids or whoever has to deal with my possessions when I'm gone. I have downsized to the point of absolute simplicity. The few decorative items I have are sentimental in nature, so I know who those will go to, and anything else is already earmarked for someone to get when I'm gone. Other than that, everything is practical and used frequently in daily life for cooking, cleaning, etc. I don't have a ton of knick-knacks like I used to, no major collections of things (other than books, and even that collection has been pared down significantly).

If you have sentimental items you think someone will want, ask them what they will want when you're gone - it's not being morbid, just sensible and avoiding any conflict or arguments when the time comes. You're just trying to make things easier for everyone. If they're willing to name a few things they'd like, make a list and tell someone where that list is so it can be handled when you're gone. Put it in a will if you have one. (And if you don't have a will, please make one...especially if you have property or finances that need to be handled.)

In the best of families, this whole thing can go very, very badly. The very family members you think will be the ones that will be kind and accepting of the situation will suddenly become very focused on money and the value of everything you had. That makes it hard for everyone else involved.