I don't mind to keep Seiya for 3 more seasons, after this year, but I'm not sure about 4 years. Seems like he's still improving. I would take 2 years for Happ, too. But, not both of them.
The thing is that they seem to be the best OFs available in the next FA. Aside from Skubal, Shota is also one of the best SPs. I like to keep Shota for 2 more years, too. If we lose him, we would have Cabrera, Rea, Assad, Brown, Steele + whoever we get before the TDL or in the winter. We don't even know how good Steele will be. If we can get a non-rental TOR guy, that would be the best.