I'm not sure I understand... so I should focus on just one character from the beginning?
You can focus on all because like Joan6969 said you only lock on 1 LI (or 2 for a throuple if happens to have that choice) in chapter 8. But there is at least 2 choices in the game that prevent you to get extra affinity points with some LI's and their lewd/extended scenes, of 1 or multiple LI's paths.
One is in the end of book 1/Chapter 4 near the end of the halloween party when on a choice you shout out either the INK sorority girls or DJ Kink aka Kindra, if you shout out the INK girls you can still keep all the LI's paths open (by this I mean getting their intimate scenes and extra points with them) but if you shout out DJ Kink and in the following choice steal a kiss from her it will at least lock you out of more intimate moments with the INK girls, Paige, Zelda, Naomi, Reina and Katy (not really sure about Katy, forgot if there is a condition on the scene with her in chapter 6) and preventing you to get extra affinity points with them.
Those are easily checked if you read Mr Bubu pdf diagram walkthrough or if you use URM and check the code on path detected points.
The other choice is if you keep going on Zelda path in chapter 5 (taking her to the airport and of course not stealing a kiss from DJ Kink) it prevents also going further with Paige on chapter 6, locking out of the lewd scene with her.
Also there is a choice in chapter 6 that either you go on a date with Reina or Katy, so I guess it is 3 choices that prevent lewd/extra affinity points.
Now what we still don't know is how Digi.B will code the access to lock on a LI path (if just the affinity points or also a condition from a variable) in chapter 8 or what variables will take into account which the LI's are available to lock on their path(s). So take all this information with a grain of salt, it just sets some variables so far and prevent you to get lewd/extended scenes and extra affinity points with them, we will see how it will play out and get coded.
Just read all the above and sorry if seems confusing

putting what is in my head into words isn't my forte, prefer numbers and statistics lmao.
I simply made only 1 split playthrough and in both I didn't steal a kiss from DJ kink, and in one playthrough I went with Zelda and Reina and in the other with Paige and Katy, and both with all the remain LI's on chapter 5 and 6.