Are there any missable/limited recruitable monsters

As Yuck mentions in his answer on whether a new game plus mode exists, each area has an item that—once retrieved—lets you reset the area and play through the events again. This allows you to pick different Live Trigger options and get the reward you missed.

As an example, once you complete New Bodhum -003 AF-, the next stop is Bresha Ruins -005 AF-. There, you'll find a key item called the 'Leaving' Gate Seal, which allows you to close the New Bodhum -003 AF- gate. Closing a gate will reset the events of the area, and thus, allow you to get the reward.

Also of note is that closing a gate will unlock new Live Trigger choices, replacing some of the old ones. Based on the list in the strategy guide, most of the replacement choices are the "funny" options, so an efficient strategy would be to get the "serious" reward first, then get the "funny" reward once you can close the gate seal for the area.

It is possible to max out every role to level 99. Once you have done so you can't level up the Crystarium any further. And just FYI the last 100 or so levels of the Crystarium are exponentially more expensive. Something in the neighborhood of 2k per orb.

Your max stats are not fixed, so in a sense, you can screw up the Crystarium. If you'll notice, when you are on a large orb that isn't a skill you'll get an additional bonus depending on what role you level at that point. So let's say you're leveling Noel and you take a COM level at a large orb. You'll get a bonus to that particular role. So although every role can hit 99 if you want Noel to be a strong COM you would want to always level COM on a large orb. In effect the number of large orbs is fixed.

Hope that makes sense.