Alright..
First question:
Based on Vit, is that how much life we gain?
Ex: 50 Vit = 50 life+ per level.
Whats the max vit we can get per level?

2nd Question:
How much is ideal str for rogue?
If the answer is as much as possible, my question is, is 120 enough?
My gear has enough so that I don't have to invest any into dex.

So, would it be wise if I put 15-25 stats into vit, then pump everything into str?

Question 1: Max Life gained is ~140 (at level 71) which is how much a barbarian would get at level 71 if he put every stat point into vitality for every level.

Question 2: This question will always be about preference, but what i can tell you is that str is always a good stat to have a lot of. While dex is also important, the more you have of it, the less an additional stat point in it will help. Dex is a stat that lessens in benefits when you have a lot of it. So if this question was: "i have 150 str and 150 dex, what should i put my next point in" i could tell you confidently that str would be a better choice. But it really is about your preference. on my chars i aim for about 120 dex and put the rest in str, but thats just me.

As for your last question about the vitality, honestly i wouldnt put more than 10 vitality, 15 at the very very most. The only reason you would need more is if you were a tank character, which would be better suited as a guardian or a barbarian. 10-15 vitality will be fine.

BTW, if you have any further questions, click the link in my signature. it will take you to a list of people on this site that will gladly answer your questions without having to post them. If you would like, pm me and i will give you my MSN address and you can message me any further questions.