Best practices for using image backups

I've just built a new machine that RAID 0s two SSDs for the boot drive. I installed ATIH and did an image backup of the two partitions created for me by either the BIOS, RAID driver, or Win8.1. I'm storing the image on the Acronis Cloud.

Questions -

1) Does the image backup grow in size as I install more apps and data? Or is it a sector-by-sector image (exact copy) of the logical device, and hence stays the same size regardless of data content?

2) Should I be periodically running the image backup? Or should I manually run the backup only after making significant changes (such as installing new software) that I've tested and know I want to keep.

3) Do image backups to Acronis Cloud use Incremental mode? I know file backups do, and there is no way to change it. Incremental image backup sounds odd to me. But it might be useful to spin the clock back and restore a known good image (much like System Restore, but deeper).

Thanks for helping me understand the best way to backup my RAID.

Keith