SPDIF cable same as coaxial cable?

Does SPDIF just take the I2S format and just change into a single connection instead of 5 connections.

No, they are two different formats.  The main difference is that I2S contains both data and the clock (separate wires), while with S/Pdif you have to extract clock from the data stream (one wire).   Yes, you can have multiple devices on I2S bus, but the main reason for it in audio is to have better (less jittery) control of the clock.

AES/EBU - uses an XLR cable that should be engineered to have 110 ohm impedance.

Like with S/Pdif, AES/EBU is an audio transfer standard and not the cable.  It can be used with 110 ohm XLR cable (IEC 60958 type I), with 75ohm coax or Toslink (IEC 60958 type II).    XLR is just most common cable with AES/EBU.

The main difference between S/Pdif and AES/EBU standards is in the property rights.  S/Pdif includes Serial Copy Management System, preventing second-generation copy in some instances.  Most of AES/EBU used in consumer audio is S/Pdif standard.  It is assumed to be 110 ohm XLR only because that was the most common use of AES/EBU (studios).

Also, AES/EBU was defined as 24 bits while S/Pdif was 20 bits + 4 auxuliary bits, but these 4 bits are used (almost always) as data extension to make total of 24 bits.

So, in consumer audio both "AES/EBU" and "S/Pdif" follow S/Pdif standard and name difference is customary for different cables and electrical levels.