Another Rockman 4 hack eh? Well, I welcome ambitious projects - but some of your ideas aren't er, good. Don't incorporate Mavericks into the classic series. If you want new bosses based on existing Megaman villains, pool from some of the net navis that don't have classic series equivalents.
Also you appear to be using tilesets taken from a hack of Megaman 2 called Megaman Ultra - which itself "borrowed" tilesets from other games such as Zelda II. It was ironic there, but using them as anything other than placeholders isn't really a great plan.
No Wily in a classic series game? Then it's NOT a classic series game. You have to incorporate Wily, even if you choose not to make him the final boss, like in Megaman V GB.
Some general pointers:
In Megaman 4, the MegaBuster charge shot was added for the first time, but it's not really that great. Don't set up your stage designs to absolutely require it at all times.
At all times try to keep the difficulty curve balanced. The robot master stages should be easier than the Cossack stages, and the Cossack stages should be easier than the Dr. Wily stages. AVOID sudden spikes in difficulty. I'm not saying don't any any challenge, but keep it in check - this is a problem the majority of the Megaman 1, 2 and 3 hacks have.
Design areas to make use of the Balloon and Wire! The Balloon is kind of like item 1 or the Magnet Beam, and the Wire goes mostly unused in the original game. so don't be afraid to add areas where the use of the gadgets are needed to proceed or to bypass a section.
Always, always design areas with fail safes. If you include an area with that you need Rush Coil or Rush Jet etc, then ensure that you're giving the player a solution if they should run out of weapon energy - a spike, a pit, a respawning enemy, something.
Add E-Tanks in tricky spots to entice exploration of your levels.
If you want to check out an example of a hack that gets MOST things right, check out Rockman 4 Minus Infinity. This hack isn't completely finished (I'm still working on it myself in the final beta stages) but it also does crazy things you won't be able to copy. Just make sure your level designs are good before you worry about creating custom graphics or music.