The Wraithlord comes with all the weapon options you could possibly want, and then some! There is two shouldermounts (I cut away the right one) so there is really no need for the hand-held mount, but GW included it anyway.
(Edit: There is only one of each HW of course, so if you want duplicate weapons you have to steal from a platform or a War Walker)
As for the pins, it may become a problem with the weapon-hand swinging around its pin. To be absolutely fixed there shoul be 2 parallell pins there, but there just wasn't any room. What I have done so far is make the pin as long as possible and bend the tip of the pin a little bit so that it presses against the walls of the hole. I'm hoping this will be sufficient, otherwise I can always replace the pin with an even longer, and make the hole deeper. I think there is still some room. If nothing else works I just have to make a choice in weapons and glue the thing on.
I don't know exactly how small those magnets are that you guys are talking about, but they would have to be incredibly tiny to fit because there is not much room on those mounts. On the shouldermount I even had to add greenstuff just to make the hole for the pin!