Bear in mind that the Hall of Monuments achievements are
account-wide -- so if you have a warrior who finished Prophecies and a ritualist who finished Factions, each of those characters can put those achievements in their hall for overall account credit. You don't have to use just one character to get all your points, though some titles make more sense to attain on a single character, such as Cartographer.
If you have a character who has finished Prophecies and/or Eye of the North, you'll want to get it started on
War in Kryta so you can start saving up medals for Oppressor Weapons. You can dedicate these to your hall. And, again, you don't have to dedicate all weapon types on the same character. Your warrior can dedicate hammer/sword/axe, while your caster could dedicate a staff. It all counts towards a full monument.
Once a statue has been dedicated to the hall, you can delete the item, or even the character who dedicated it. The achievement will remain.
This is probably all covered in our
Hall of Monuments Guide , which I urge you to read.

Once you understand how the Hall of monuments works, and what you need to do to acquire the points you desire, you can determine which of your existing characters will help with that and which you can let go if you need the extra character slot. Overall, existing characters will be more helpful in filling your hall than fresh ones. Secondaries can be changed. Makeover packs and name-changes can be purchased if need be. But it mainly comes down to what will give you the most
joy.
Welcome back to Guild wars! Good luck!