Your current team isn't bad. If you have good breakthroughs on Hashirama tho (+1 mystery and Y passive that makes him immune, the others are nice but not as necessary), I would say probably put him in instead of Roshi:

Using Death Mirage instead of Bani Chakra means you can't mystery with Kushina round 1 unless you get up Hashirama's barrier early and steal some of your opponent's chakra with it. Imo this isn't a big deal, but if that bothers you you can switch to the chakra passive.

Another team with Izuna, doesn't have as high of buffs as the other one suggested earlier but it's a bit safer in terms of keeping off debuffs.

In terms of ninjas you should grind for. 4* Kushina is always nice to have but she's kind of falling out of meta. Imo your top priority should be getting GNW Madara 4* star to get his breakthroughs. Otherwise, tbh I would just wait until SOSP breakthroughs come out. So start collecting SOSP Naruto frags when you can. Tbh I believe that when those BT come out, most other pos 1 ninjas will become irrelevant. GNW Madara can semi-counter him I guess, since with Nagato (BT only tho) you can make his mystery unmissible, it does more damage to jinchuriki, and you can make his chases unmissable too which gets around Naruto's chase dodge BT. I don't really see the other ninjas that are meta right now (BT Kisame, BT Kimono Shisui, BT Edo Minato, BT Kakuzu) being too useful when SOSP BT comes out (probably in a few months, like 4-5 months) because he just outclasses them. I think GNW Madara will maintain some relevance tho since he can be a support as well, people might run him pos 2 on SOSP teams.