You don't have to run your node 24/7 to be a full node. You'd need to keep bitcoin ports open and make sure that your node is syncing every time you start it. If however, your node's syncing time takes longer than your node running fully then it'll might be a bigger burden to the network rather than a contributor.
Also, if you have a good connection, consider downloading the blockchain files from an updated torrent in order to dully take advantage of your download speed without having to run a full client at the same time.
Seeding blockchain files does not directly help Bitcoin. As of 0.10.0, Headers-first synchronization is already implemented and the Bitcoin core synchronize from different peers simultaneously, hence, it is much faster to synchronize directly from Bitcoin Core client. Even if you want to seed the torrent, it won't be updated and users still have to manually connect to nodes to synchronize them.