Ok, I've been pretty busy with exams over the week, but it's my midterm next week, so I should be able to devote a day to the hack before studying (I've exams the whole week after the midterm break, too).
Item-sprite insertions.. Are generally the same as Pokemon sprite insertion, with unLZ. However, I'll leave that until you've knocked everything else out of the way- the last time I edited an Item-sprite, apparently the game glitched when the edited item was selected in the menu (it was for a hack by Mervyn797, I edited Oak's Parcel into a Laptop, didn't change the palette or anything. I gave it to him to insert, and he said the game froze. So.. It's just a matter of backups and such, but it'd be easier to leave until just before release time, if you have any idea what I'm talking about:D).
That Chatot.. Shouldn't be a problem, of course. I mean it's my job, right? It's cool that you're referencing Mystery Dungeon 2, though. I've only played Darkness as far as where you actually join the guild, but it's generally a cool game. The story is better than the Red/Blue Rescue team story, anyway, so it'll work out well with Hidden Ties' story (which is brilliant already, if I haven't said before:D)