My opinion, go for Shisui first .. Shisui is a good support/frontline ninja .. His standard attacks is insane as long as his barrier is up and his equipments are stacked well .. The other ninjas that you're gonna need are cheap ones, Itachi Anbu and Iruka is enough for Shisui to be a beast .. Kushina on the other hand, even you have that good amount of fragments of her, just continue piecing her when an event opens up where you can get her fragments for free or if the event has a setup like Great Plates, Kushina without proper support will fall easily, and her support is not cheap (sakura sailor) but you may opt to choose Kurenai too .. Kushina is not Clone-Proof and this is a waste especially if you get matched with WindMains with endless Clones .. Masked Man is one of the best support and the only ninja i find good on making an opponent go under chaos, 4th Raikage, Lightning Main under Lightning Armor effect, they all go no no when get chaosed by Masked Man ..

I have Masked Man and Shisui and I would definitely say your priority should be Shisui > Kushina > Masked Man.

As much as I like Masked Man, he's kind of weak and as soon as you've used his mystery he basically becomes useless. There's also so many ninjas that provide immobile with their chase nowadays so you don't even need that from him. Also I don't think he fits in very well in the current meta.

Maybe he'll get more useful as people start using the new Jinchuriki ninjas, time will tell.