Need help on my Jack X Bubbles fanfic

So I've decided to write a Jack O'Lantern (GAOBAM) and Bubbles (PPG) fanfic and I've got some of the story down so far I just wanted some opinions on those of you who have been writing fanfics for a while (this being my first fanfic...well sorta I've written some before but never posted them but w/e) to give me some advice and review if the story is even good.

For now I just want to know if this is a good enough premise for the fanfic. Criticize all you'd like but please no flaming on how this pairing doesnt fit well or how wrong it might be. If you dont like it, don't read.

Well anyways the story will take place on Halloween four years after the events of Billy and Mandy's Jacked up Halloween. Jack is in Hell and causing so much trouble pulling pranks on other demons that finally HIM has had enough and strikes a deal with Jack. HIM's not one to do all the work when it comes to ruling the world he much rather have a puppet doing all his deeds, so he agrees to let Jack return to earth and gives him a numerous amount of power which he can later use to get revenge on Grim, but before he can kill his nemesis he has to dispose of the only thing keeping HIM from ruling over the world...The Powerpuff Girls. Meanwhile Bubbles has gotten out of bed to get herself a drink of water and when she returns to her room she notices a strange mist that soon turns into the form of a strange Pumpkin headed man.
I plan to take my time with the series making the relationship between Jack and Bubbles steadily grow rather than have them be a couple in the first chapter. It will probably feature some Cartoon Network characters from other shows. The characters I do plan on having for sure are:

The Powerpuff Girls
Jack O'Lantern
HIM
Grim
Billy and Mandy
Nergal

Well I'd like to hear from others what they think of this. Is it a good idea or do you think it will crash and burn?