The Hall of the Novice (Beginner's Hall) should be accessible from any of the 'Smith' npcs with the big green sproutling icon which can be found in the Adventurer's Guilds in each city (the Gridanian one is positioned between the Inn counter and the repair npc).

As for questing, definitely keep up to date with the class quests given by the Guildmaster for your class's Guild (E-Sumi Yan at Stillglade Fane for CNJ), as it not only unlocks the Armoury System after completing the level 10 one (which allows you to change classes), eventually after completing the final class quest at level 30 you will be able to then unlock the Job upgrade for that class (in your case, WHM for CNJ). The Job upgrade also requires you to be past a specific level 20 main scenario quest though so once again keep plugging through the main scenario, it does get better despite dragging on sometimes (and it does draaaaag a bit).

Also in regards to the posting restrictions, that is connected to your current in game level, as you gain higher levels your posting restrictions are reduced although sadly they are not completely removed. This thread explains the restrictions and what levels they are relaxed.

Either way, don't get discouraged! Also, Welcome to Eorzea!