Your baby will naturally fall asleep when in a wrap, as they feel safe and the sound of your heartbeat and gentle movement will relax them.
Babies naturally sleep for a long time so do not be concerned if they spend the majority of their time in the wrap asleep. This is ok as long as they are in a safe, secure and comfortable position.
As baby gets older they will sleep less during the day, up to the point where they will naturally transition to not napping at all.
Unless you have reason to do otherwise, it is absolutely fine for baby to nap in the sling, many people choose to use them as a tool to aid with napping. This will not create problems later on.