As with what others said, pick a codex. That will help us to give you sound advice.
Lots of DA stuff? Like the Dark Angel theme? Get the DA dex. I dont own the DA dex, but if it is anything like the SM Codex, I would equip my HQ with a relic blade as opposed to a regular Power Weapon to give him more power to kill tougher things.
If you go with a SM codex and your boy loves dread, see about getting him the Master of The Forge, who allows you to take Dreads as a Heavy or Elite choice.
Definitely get another squad of basic Tac Marines. If playing against lots of orks, a Thunder Fire Cannon is a good choice.