Unipolar means there is only one TVS diode, meaning it will conduct normally one direction and bidirecitonal means two back to back TVS diodes. So bipolar will clamp a line symmetrically above and below the the ground, and unipolar will clamp assymetricaly (it will clamp within breakdown voltage above the ground rail, but below the ground rail, it will conduct like a normal diode and clamp to the forward voltage of the diode so it better protects unipolar systems).
Power for ESD...get the smallest one you can? THe energy is so small in an ESD pulse because it's so transient so it does not have a continuous rating. It's kind of a black art to be honest with different ESD waveform shapes and shocking scenarios.
You do not need a resistor for ESD...the energy is so short that the diode can dissipate the heat all on it's own. A resistor would add additional protection though because unlike the TVS diode that has to switch on to protect the circuit, the resistor is always "on". Another result is that it allows for smaller TVS diodes to handle larger transients. But for ESD, don't worry about burning up. It's not for continuous or heavy energy clamping like other overvoltage circuits.
As for standoff voltage or working voltage...there's a difference between that and breakdown voltage. Breakdown voltage is what it the TVS clamps to but there are manufacturing tolerances of the breakdown voltage and breaking down also isn't a clean-cut threshold (you don't want the diode to be semi-breaking down near the extremes of operation). So there is a gap between the breakdown voltage and the regular operating voltage rating- this is the standoff/working voltage.
They can be used for analog, though depending on the signal they may affect integrity (like adding stray capacitors to RF circuits). It tends to be fine for most hobbiest level applications though (you're not running RF or MHz serial signals right?)