Hi Alan!
So: I do know that Overworld Manager may cause some issues with palletes in AdvanceMap. However, this shouldn't affect what you see in-game. The palette of your sprite may be messed up in AMap but when you're playing the game, it should be okay.
I don't think this is an issue with Overworld Manager, but with AMap, since AMap is not configured to handle all of the extra palettes that Overworld Manager adds to the game. If you can get past this quirk, everything should be okay. As a side note, you do not need to index your overworld sprites with IrfanView when you use Overworld Manager--it will do the indexing for you.
I don't really understand what you mean by "the player's sprite is standing at the place of my new sprite." If you could clarify, I might be able to help, but of course no guarantees.