i can't really tell what exactly is important but i can describe what i had in my game, when i got ending 4:
-relationship to Ellie was higher that the relationship to Paul
(i don't think thats important, you only need it high enough with both for the threesome evening)
-all sexual skills at Pro
at the threesome evening: kiss, let Ellie give Paul a handjob and let him cum
(if you choose something else you can only get ending 2,3 or 5 depending on your decisions in the bedroom, best keep your triggerhappy fingers away from your mouse, or you might accidentally click the "stop her" button)
-the activities in the bedroom after that seem to have no real influence on the ending, i got ending 4 for all possible decisions
(you can making Ellie stop sucking or fucking for an aditional anal sex scene)
Some kind of walkthrough,
i suggest you play the hacked version, it makes it less important
to always make the most efficient decisions for the increase of relationships, because you can always rewind the time.
the m key sets your money to 777, it will also decrease your money if you have more than that
more important are the 1 and 2 keys, try not to decrease days at weekends or directly after you had an story event
(to avoid event bugs)
don't worry about the weekdays not changing when you reduce the day number,
that fixes itself for the following day
Increase accounting and fitness to at least 20 (fitness in the park after you got to 12 at home),
keep morale high by chilling in the park
earn a bit of money by helping Ellie at 12:00 in the shop and/or working as an accountant
(12:00; 15:00 and 18:00, at 18:00 you get more money)
after some events you can also work in the pub at 21:00 for the biggest money increase if you still need money then
(you need 20 accounting for that)
i would decrease the day from 2 to 1 until you have the personal stats and the money you want,
(each tuesday at 21:00 press the 1 key once then play another tuesday and again press 1 once...)
that way you have enough time to get all the events without worrying about missing some
after that, reduce the days to 1 again
Timetable Ellie: 9:00 living room, 12:00 shop, 15:00 cantina, 18:00 living room, 21:00 bedroom
Timetable Paul: 9:00 unknown, 12:00 office, 15:00 cantina, 18:00 subway, 21:00 pub
the first chat option is always available, all the others have a minimum relationship to give a positive effect
above 5 relationship most of the second chat options are available
third and above chat options can have very different requirements depending on locations
(10, 20, some up to 100)
you should avoid shopping at the beginning, because most of the stuff gehts you big relationship increases and at the beginning the first limits in relationships are rather low
(wait until you are above 20 relationship)