Sorry for the tangent above, just very inspired by what you had down and wanted to get the whole thing down before I forgot.
Adding a sack of 30 hp to the field at level 1 is big. Probably too big. The limits to healing it are okay, but it looks like Mending brings it to full. I might look at the Battlesmith Artificer and how mending heals their Steel Defender.
The Catapult spell is fun but I'm not sure if this is supposed to be your primary method of moving the sphere around. Maybe I overlooked it, but did it have a speed on its own?
I had a sorcerer origin based on the Sphere of Annihilation, I'll post a link and you can mine it for ideas if you like. If you really like it you can buy it on DMs Guild.
Free
Paid