You are not required to carry 11 prospects but you cannot use any vacant prospect/minor spots for NHL players unless said player meets the prospect requirements.
Each team will also be allowed a prospect, or junior team as well to farm and develop prospects. The prospect roster will consist of six maximum players in the inaugural season. Prospect players may be active NHL players but must be under 25 years old and played fewer then 25 NHL games. Prospect players can be promoted to the active roster one time only. Once a prospect is promoted, he may not be demoted back to the minors. Essentially a prospect is any player drafted by a NHL team and is under the age of 25 and under 25 NHL games experience.
If a team promotes a prospect, acquires a player via trade or free agency/waiver etc and is over the maximum allowed number of players you must immediately select players to release as free agents to become roster compliant.
After the inaugural draft there will be a 3 round entry draft each off-season. The draft order will be based on reverse order of standings, with 1 exception and that being the bottom 5 teams will be placed into a lottery. Each draft will add 5 more roster spots to your minor team, up to a maximum of 25 players. This will allow you to draft your prospects and allow them time to develop. Just so everyone is clear you don't have 25 minor spots now, you have 6. After the 2013 draft you will have 11 spots, then after then 2014 draft you will have 16 spots and so on.