If you are able to gain a second CR +1 template, after becoming a Lich, you could become an Advanced Creature, and as such gain a further +4 to your intelligence, amongst your other stats.
Combined with advancement to Venerable age, which can be seen on this PRD page, which nets you a further untyped +3 bonus to your intelligence, and the methods mentioned in your question, you will be at a plump total of: 18+2+5+5+6+4+3 = 43 Intelligence
Then, if the Mythic Adventures rules are used, and you ascend to the lofty heights of Mythic Rank 10, you can receive a further +10 bonus to your Intelligence.
Combining this with the 3rd tier Path Ability Enhanced Ability, nets you a possible maximum, without adding any other templates, 55 Intelligence ability score!
With a measly -2 on your Strength / Dexterity / Constitution ability scores after ability score generation and racial modifiers, and a +7 on your Wisdom and Charisma!
If the wizard in question somehow also gains control over a Succubus, or is daring enough to strike a deal with one, then they can also gain a +2 profane bonus. (Although I would very much encourage any player willing to do this to consider the implications of a Succubus having direct telepathic access to their minds!) This would get you to a net total of 57 Intelligence!
That's a +23 modifier?! Yeesh!
Note: Not many DMs will allow you to take so many templates, but those that do are probably applying them or using similarly terrifying encounters against you, so be warned!