I've been using flickr for a long time... 13 years or so. In recent years flickr policy changed in bad (delete photos for free accounts). After all what can we expect from a company that needs $ to suvive. Is not their fault. But is there any good solution less pricy than flickr to safely store tons of photos?
It might depend on what limitations you can be happy with, and how much storage you'd use. Don't forget there's a free gallery for Yashica Forum members, if it might fit what you need... yashica.boards.net/post/5573/thread
The few alternatives to flickr that have free plans available can be pretty limiting, and if they also have 'pro' plans, they can get very pricey. There's a short article with a summary of 10 alternatives, and there's always the possibilty of self-hosting your own gallery on a site you own by using free or low cost software. (I'd be happy to help with that, if you'd want to go that route)
That's a sizeable amount of them to store, and I don't think anyone offers anything that's free and offers some ownership protection for what you have. Of the 10 alternatives in the linked article, I think the pro plans offered by either 500PX or PhotoBlog would be the most reasonable cost-wise, but I don't know if either one has a bulk import option. That might be a real issue considering the time and work to get them in and organized.
400GB isn't a cheap alternative for self hosted solutions, unless the actual storage takes place with a cloud storage provider. There's Chevereto's gallery (the same one used by gallery.yashicaforum.net) that has both cloud storage and bulk import. It wouldn't be free, but would be reasonably cheap to do.
I stumbled upon a site that might offer an option at low cost image hosting, but it isn't exactly an alternative to Flickr's style of public browsing and searches. Zenfolio is a platform geared to pro photographers, and specifically those that need things like online appointment-setting tools. All their plans offer 'unlimited' uploads, and even having your own domain name to point to. There's a 50% promotion until Feb 21st, too.
The problem about the online albums is that nothing online last forever, and having a photo album with thousands of pictures well organized requires a lot of time and efforts, and it is not something easy to migrate from one service to another when something happens, even if the services allows to download all your pictures, like Google Photos with the "take out" option, only recovering the metadata related to each picture is a nightmare (name, comments, annotations, location, etc).
The online services are changing more often than before, not only the policy and conditions, also changing hands like happened with Flickr more than once in a few years, so we know for sure that the nightmare of migration to another service is just around the corner.
If you want to have an online album that is 100% yours, under your control, and being you who decide what information to share and what not, then the best option is to create your own service, it could be via a hosting service or even better in your own small server at home. It is not so difficult, since long ago that small and powerful computers are available very cheap, like the Raspberry Pi, and also the price of storage dropped a lot, so buying a big hard disk is not as expensive as used to be. And for the software to create a photo album, there are few FOSS (Free and open-source software) options, like Piwigo.