Yes, Chrome can be difficult to get rid of.
First, install Lightning, and thoroughly go through the settings.
Get used to swiping left to go to your bookmarks, ans swiping right to go to your open tabs.
Then...
Go to
Settings
Apps
(show all)
(show system)
Chrome
Disable
If you cannot disable it, then tap Uninstall.
It may only allow you to uninstall all updates, or whatever.
That is fine- get rid of what you can.
Now tap Storage on the Chrome app page.
Delete all data.
Now, back to the apps list, and find Lightning.
Scroll down and tap Advanced.
Select Browser App, and choose Lightning.
As for your photos, are they all stored in the phone memory, on Google Photos, or a combination of both?
Do you have a computer?
Here is the issue- your device has limited storage space.
Unless you make your SD card the default storage (NOT recommended), you will need to download chunks (whatever will fit comfortably) into the phone memory and then transfer that to the SD card.
To make matters worse, it is advisable to copy, rather than move files, to the SD card- and then delete the files on the internal memory.
This is an added precaution (that I rarely follow myself) to ensure that you do not lose or corrupt files while transferring.
Tedious?
Of course.
But if you have pics and videos that are valuable to you, then it is worth it to ensure their safety.
As for Google Photos, as long as it is working for you, you don't need Chrome to keep using that.
Online storage is yet another way to ensure that you don't lose any memories.
Think of it as another backup.
Now for moving files from device to device, I use NitroShare.
It is extremely easy to use, and it is wireless, as well as being fast.
https://f-droid.org/en/packages/net.nitroshare.android/
https://github.com/nitroshare/nitroshare-desktop
Once you get a workable size of data (ie. it fits and leaves enough room for the device to function properly) onto your device, use your gallery and/or your file manager to move the items onto your SD card.
This is also as good as time as any to categorize and file them all properly, so that you can find them when you want them.