I also modded culture:
Amphitheater: +2 [+4 with a great work, very rare]
Opera House: +4 [+6 with a great work, very rare]
Museum: +4 [+8 with two great works/artifacts, kinda rare but happens]
Broadcast Tower: +6 [+8 with a great work, never happened lol]
Also, when I get the Mosque-Cathedral [a modded wonder], all temples empire-wide yield +2 culture.
Add pagodas, mosques and/or monasteries from religion, I can get an extra from +2 to +6 per city [it is rare and requires some effort, to convert to foreign religion,get their religious building, than convert back to my own, multiples times per city, to do this particular trick].
Usually I can fill at least 4 policy trees, plus get a lv3 ideological tenet, before the game ends. I like to go Tradition + Liberty + Commerce + one of the victory related trees: Patronage [diplo], Aesthetics [culture], Rationalism [science] or Honor [domination].
PS: whatever the victory, I almost always make an effort/compromise in order to get at least 2 in Rationalism. Its just too good to pass.
PS: I tried a diplo game with Piety+Patronage openers once, thinking about going Commerce as 3rd, for massive CS bribes. Never again, I swear to God... being on the short of the science stick is horrible!