*facepalm*
First of all, getting rid of offtopic things, SRB2Unleashed was made during 1.09.4 era and was too far in development to just change to a new system when 2.0 was released.
Now that that is out of the way. On to your rant of the levels being the same.
I'm sorry, but that would be impossible as Sonic Heroes includes many things that are impossible in the current build... wait sorry, I'm wrong, impossible in SRB2, ever. These things include loops, excessive use of bot destroying to get to the next area, advanced slopes, switches that make things appear, casino areas (I will admit, that would be awesome, but not good enough for the amount of effort to put it in) and robot AI and features. No matter how you edit the code, you will never get a level like a Sonic Heroes level without going to something like that BlitzSonic engine or something. The levels are also thin and won't compliment the layout of SRB2 levels and the amount of exploration that SRB2 is made for.
There can be areas which are slightly similar to in game level areas, but other than that, sorry, no. The levels wiill not be made exactly like the levels in Sonic Heroes.
The Character WAD question though. Of course you can add character wads in, you can always add character wads into anything. All it does is prevent you from saving since you're technically cheating. :D
Okay then.
I haven't played this in a long time, so I can't remember how the levels were. I would still like to help out with the project, heck I would even compress the music for you or those silly little level theme things I did in GFZ. XD
So if you need some criticism in level design or some random sketches of concept art, I would be happy to help.