Everything allowed, from the creation of own Mystcraft Ages to the placement of EVERY block. No restrictions. You should note though that you are at least 18 years old.
Hope seeing you on the server!
Steps to accces the server:
Download the Feed-The-Beast launcher at http://feed-the-beast.com
Select the modpack you wanna play. In this case Direwolf recommended version.
Login with your minecraft username and password.
Press the launch button.
Go to multiplayer and connect to modscraft.eu.
If you have any problems with this or have a question pm me :)