As far as the hall of monuments go, they have revealed a little more on it from Gamescom a few weeks ago in germany. First: there will be an article coming "soon" on the gw2 website that will include a full hall-reward guide.
Second: various accomplishments, achievements, statues, etc will accumulate as"points". With these points, u will buy/unlock various rewards in gw2. Finally, you do not have to have a full hall to receive rewards.
**speculation from here on out**
With a point system, it could be implemented in a number of ways: each unique item/title/statue added in your account gives you a point, and various levels of stuff become available as you meet and pass point levels.
It could accumulate based on a total number, on a per monument grouping toward related rewards, or some combination between. Going further, certain achievements/acquisitions could give different point values. For instance, a treasure hunter title could be worth more points than say, a guardian title. A special event green minipet might be worth more than that white jungle troll you got for your first birthday.