This app was mentioned in 4 comments, with an average of 1.25 upvotes
No, HTC Camera.
Should work, as for risk.... well if you don't follow instructions I suppose you could brick your phone, although you can usually go back and start over again as long as you're working with ADB to push updates and stuff.
I didn't spend very long on Sense to compare battery life, so I am not sure I can answer that well for you. My wife had the M8 before I had to give my Nexus 5 to her in exchange for the M8 (her hands were too small for it) and with her minimal program installs and use she was getting almost 2 days (GPe) worth of battery life. I however have a lot of programs installed and use mine pretty heavily. I get a full day (~12 hours) worth of use out of it and Battery Saver can help stretch that even further.
I do suggest you install the Sense Camera and HTC Gallery after, the Google camera is too simple and is missing a lot of features that HTC has built in. The capture is quicker using it (the Duo camera is used while in Google Camera it is not) but the quality of the photos is very similar.
What photo app? I have a HTC One M8 with this photo app
Try installing these: https://play.google.com/store/apps/details?id=com.htc.camera
And
https://play.google.com/store/apps/details?id=com.htc.album
I'm not on 10 but running a custom 10 ROM on my m9. See if these work for you.