Rather than painting a picture, it throws up questions.
As for their dimensions, they'd have to be disproportionately thicker than a simply enlarged human, as strength of bone increases with its cross-sectional area, but the burden placed upon it with the volume of flesh. Hence, why elephants are so stocky.
While quite single-minded, with a sole purpose, sole course and thus sole dimension, this is a very tragic character - and may even be suitable as a protagonist if one adds a desire to combat the madness and goals beside killing.
What you might add are details of his schemes, how he goes about his quest for vengeance, for personally hunting a cult spread amongst the stars is stylish, but ineffective.
Well, DnD is full of trap-creatures like mimics, man-eating walls and floors and pants that are basically defeated by one roll to "sense whether there is something amiss" - if you don't you're screwed, if you do, the trap-creature is a sitting duck.
Thus, I suggest re-making the bush into something more original. Keep the name, but perchance... what about a sentient labyrinth of shrubberies, for example?
So far, a 2/5.
Well, I like the back-story - though the telepathy thing takes a lot away from the possibilities. What if it had to resort to human senses to find out the murderous scum? Stalking, observing, judging, analyzing, before deciding to move away or in for the kill.
It could even improve its effectivity by instructing others to follow its path, a cult leader of sorts, or the founder of a philosophy...
Lots of potential, but much of it untapped.
Well, a nest of them seems to be worth the nuke, a single one, as written, appears in the flamethrower-plasma grenade-HEAP missile range;
Unless the demon part inside gives it more resilience and strength than anatomy would suggest, and as it appears to be able to hide in sewers, hence, is not huge, I'd place it as a threat like, for example, the Starcraft Hydralisk: can rip up an armored car, a tank will shoot it to bits.
It is good that you brought the topic up, but generally, I found applying dice modifiers to love unnecessary - players who care about the characters and NPCs enough to be bothered by the concept of love will act it out - and sometimes deliberately fail rolls; likewise will they succeed without rolling against fear and the like when their loved ones are in danger; often these scenes will be entirely roleplay and no system.
So, good idea, but approach it from a different angle.