I believe that everyone is already aware of Google's tracking records as one of the most privacy-invading company of all time, given their terrible privacy policy, business choices, and ongoing user tracking. However, Google does have certain products that are pretty good, like Google Photos app is one of its better ones. I can see why people would use it It's quick, packed with incredible features, and makes finding photos simple.
However, it is awful for privacy given Google's track history. Recently, though, I found a upon a fantastic alternative called Ente. With real privacy and it doesn't steal your data, it offers nearly all of the features of Google Photos. It is open source, features easy sharing, end-to-end encryption, and allows you to view, organize, and download your data in its original quality across all of its platforms with consistency.
Unfortunately, if you are someone who frequently takes images and has pictures of years and years worth of stuff, you may have to pay for more storage, although the costs are not too high. To minimize space while using Ente, I would consider copying a bunch of images to an external hard drive or SSD. You can also delete unnecessary old screenshots or photos that you don't want to keep saved in your memories to save up storage.
It is a great idea to move away from Google and move towards hosting your own services. Ente looks like it could be useful for many people to begin that transition. I will point out some common pitfalls to watch out for. But don't let them stop you from making this transition: Google has most of these same risks.
As a private, for-profit company that offers its own hosted services, it will always face a conflict between the features it includes in its "free" self-hosted version vs. its paid offering. Most companies that try this eventually sell out, either by changing their offerings or by selling the company to another one that is looking to reap some quick profits.
If the company goes under, so do your backups. All your photos. You may run into a situation where you lose all of your photos or where your photos are basically held hostage with an exorbitant export fee for that one last cash grab. For this reason I would suggest prioritizing using something like Ente as a *self-hosted service ". If you do your own backups right then you will never lose your photos.
You will have to pay close attention to the project when you seld-host. Unless you are particularly good at network and computer security, your self-hosted instance will be able to poke around your computer or network if it wants to. You are trusting the project to not eventually include any spyware (they often call it "telemetry" nowadays) or worse. So basically... pay close attention to the project's community and news and be careful during upgrades.
Do begin learning security best practices. You will avoid a lot of pitfalls by running your services on virtual machines with their own IPs on your network and good (highly restrictive) firewall rules. This isolates your application from the computer it is running on and from sniffing around your network in the case where it does something shady.
Good backups are kind of difficult. For this reason I recommend many layers of redundancy both in terms of multiple copies of data and in terms of backup process. 3-2-1 is a good baseline where you have at least 3 copies of your data in at least 2 different mediums and at least 1 off-site. Your backups should be periodically tested by doing a mock restoration and checking the output for "correctness". This is a lot of work. But it is also the only way to properly do it without leaving responsibility for your data up to a third party that you almost certainly shouldn't trust with your security or even just not losing your data, eventually.
For specific recs, I think the backup process is the most important. Anything that automatically syncs your phone photos to your own server and then makes multiple backups to multiple locations (including an encrypted copy in the cloud somewhere) is a good start. There are open source sync apps and servers, Nextcloud, Immich, etc that will automatically copy your files to your server. Then you should back up your photos using software intended for the purpose. Rsync, Borg, etc. I recommend storing a copy of your photos in a cloud service as well, like one of the many S3-compatible services out there, but only if you encrypt your data first. Borg and similar programs can make encrypted copies of your data that you can then safely upload to a cloud service.