First you just jumped 2 OSs and 2 models of device, things are going to be different. It would probably be more useful to list the things causing you problems in hopes of finding solutions to those issues.
So far you want to be able to attach a picture to a calendar event. I didn't even know this was possible so I had to go and try it for myself. For me it seems that only recently uploaded pics to Google Drive were available, and you're right, that wasn't very helpful since Google stopped using Drive as a photo backup location. Next I went online which lead me to this exact question at Google Calendar Help. It seems the only way is to upload the image to Google Drive first. Someone also suggested that you could simply attach the link Google Photos creates and attach the text link. That would require the people you've shared the event with to click on the link. Not ideal either. You can find this discussion in this link...
https://support.google.com/calendar/.../8689899?hl=en
Best of luck with your new device.