You can fill whatever positions you wish during recruiting. There is no limit or requirement to how many players you must have at a certain position. However, when it comes to changing a player's position you must have enough players remaining in his former position to fill the minimum slots. IE, if you have only one kicker you won't be able to change his position, etc. As for your receiver threatening to look for another program - if he sucks then more power to him, leave. That will open up a scholarship for your upcoming recruiting season.