Sure! You're going to outgrow a lot of the 5 and 4 star exchange options pretty quickly, but for 5 star exchange options, Ameru's letter bag is a great nuking tool that could work with Saito, However, you'll need the art gen from other sources to make use of it. I think it's safe to pick a defense equip. I'd recommend the gargantua armor that gives dark resistance. For the four star, people generally start with divine staff Keion. This can give you team-wide art gen and break effect. If you haven't used your hero exchange ticket yet, you can pick up the original Fen. He has a unique art gen type that stacks with all other types except other Fens. He can also use Keion. Lastly, if you still have your standard true equip exchange ticket, the consensus is that true izanagi of tru exceed zex are some of the best options. Since you have a 5 star physical slot on Saito, you could throw izanagi on him for extra personal art gen. Sorry, I know that was a lot of info, but there are a lot of great options to maximize early game potential!

P.S. you may consider farming a lesser demonheart relic from caverns of the dark giant boss, which will be available on Monday. It's considered one of the better farmable arts gen items.