The first example is incorrect. The second and third examples are both correct. Which one you use is mostly a matter of preference, although a hundred appears more frequently than one hundred. There is also another form, an hundred, which was common in the past, but has mostly fallen out of use. See Google Ngram Viewer: a hundred, an hundred, one hundred:
You typically wouldn't use either phrase for meetings. 'One-to-one' is rare and often technical in any case, you might say, 'On most websites there is a one-to-one relationship between a username and an account,' meaning that there is only one username per account, and only one account per username. As @FumbleFingers said, 'one-on-one' tends to suggest physical activity, or at least ...
How one and one's is different from other indefinite pronouns The possessive of one (one's) is formed the same way as the possessive of other indefinite pronouns, such as someone (someone's), but it is used a bit differently. For most people, one is consistently used with the possessive form one's.