You will be able to manipulate things that are directly your element for no malus on success rolls, but everything that is not your element will involve a penalty.
Say you chose weapons as a whole, and you want a steel zweihander, for legendary purposes. You would get -1 for specifying weapon, and -1 for specifying material, for a total of -2 to your roll. Choosing to summon a zweihander of unspecified material, or an unspecified steel weapon would only give you a -1.
((As far as I can tell, if you say your affinity is 'iron swords', you can magic iron swords for no penalties, but anything else is nigh impossible. If you have 'iron' or 'swords', you can magic iron swords for a -1 penalty, but you can do more, like iron stuff or sword stuff. If it's 'weapons' or 'metal' you can magic iron swords for -2, but you can do much, much more, like other weapons or metal stuff.
This is my interpretation, and I'm just going off the main post. It could work differently, so I'm not going to say "THIS IS HOW IT WORKS", but it's the impression I got.
The trick is finding something that's not too specific that it's useless, nor too general that you can't cast anything. If you're creative you can get around the limitations and do really cool things, like the bigass eldritch Aetherstorm we have terrorizing the forest right now. ((Can someone please deal with that before it grows to consume the whole map? Please?))
So, to answer your question, you not only would get a malus to things that deal with weapons, if your affinity was, say, 'Excalibur', you could do
nothing else other than interacting with Excalibur, because your affinity has to interact with your spells in some way.
Again, I'd wait for the GM, but this is what I believe the first post says.))