I started a third play through first time in +1 year and I found out that you can have many simultaneous fauna culling and destroy sentinel missions. I'm not sure what's the mission limit, but it's at least 70.

I jumped dozens of systems while traveling to Eissentam galaxy center and accepted any such missions, then I only had to kill 15 fauna, 2 predators and few waves of sentinels no matter how many missions I had accepted.Most missions such as pirate destroying, delivery, scan etc missions are location dependent so they can't be completed simultaneously.

I shat myself at 1:15 when all of the mission completion sounds played at the same time very loudly.