Is GPL WP Legal, Will I Get Sued If I Use The Items?

Yes what we're doing is perfectly legal, we only host items that are released under GPU/GPL license.
We have subscriptions on 30+ premium GPL vendors right now.

So far we have received 3 DMCA/Copyright notices that we counter and we win them all.

It turns out the vendors release their items under GPL license without knowing that it means we have the rights to distribute it.

There will be no one will sue people who use GPL items, because you as the user are protected by GPL license itself.