I don't understand what you mean by "its a 3f game".
Safe strings... well even if a move is safe, you still usually end up in disadvantage if your attack was blocked. So if you finish a string, it was blocked, and then you continue to attack, you run the risk of getting countered. Did you already know this?
Okizeme is wakeup pressure... I never cared about the definition myself, I just started doing it without thinking.
Basically you want to hurt the opponent when they remain on the ground, to force them to get back up. For that you want a low or mid attack that hits grounded opponents. If your chosen attack for that does not track rollers, you need another attack for the purpose of hitting grounded rollers.
When you predict that they will get up, you want to hit them with a mid or low attack once again, this time to force them to block correctly or suffer the consequences. You want to make it hard for them to block correctly, so use relatively quick attacks.
When people tech roll, they can't block anything for a little while, so you can "trap" them by hitting them before the tech roll recovery ends. I can't really go in more details...