[color:"orange"]What is the maximum level you can reach by the end of Planescape Torment[/color]
There is no level cap in Torment. But I've read things get glitchy around level 128. There are areas where the creatures respawn. The best of them is UnderSigil later in the game. If not using the Fix Pack there also a few infinite experience loops in the dialog.

Fix Pack
http://planescape-torment.org/

[color:"orange"]I thought I recalled someone mentioning level 25 as about the maximum level[/color]
Level 25 doesn't refer to leveling up. It's the highest you can raise your stats to.

[color:"orange"]trying to get that perfect roll with everyone when they level up[/color]
Max Hit Points
http://www.planescape-torment.org/mods/readmemaxhp.htm

[color:"orange"]and as a warrior int is useless[/color]
Don't ignore stat checks.