It is possible that the singular/plural choice is not a purely syntactical matter, but partially depends on whether the speaker's focus is on one or on more. If it is expected that there will be more than one (and one is included just to cover all the possibilities), it is natural to use the plural.
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 ...