ESR and CSR of Capacitor
Is it be correct to say that the CSR = ESR + external resistor = 1.3 + 0.5 = 1.8 ohms? 


According to a footnote in the datasheet, "CSR(compensation series resistance) refers to the total series resistance, including the equivalent series resistance (ESR) of the capacitor, any series resistance added externally, and PWB trace resistance to CO."

In most cases, the trace resistance will be small enough that you can ignore it, and your formula would be correct enough.


  Now I would much rather use a ceramic cap, which from what I've read, has an ESR in the milliohms. 


Remember that a ceramic cap in the 10 - 15 uF range is going to be fairly large, which can cause reliability issues (due to mismatched CTE between the cap and board).


  It looks like a CSR of 0.1 to 2 ohms would be sufficient.


Notice, comparing figs 28 and 29, that the required CSR changes depending on the capacitor value.

And your capacitor value will change depending on voltage and temperature. But 1-3 Ohms total resistance seems to be okay for any capacitance value.


  If I use a ceramic cap instead of the tantalum, and if I add an external resistance of say 1 ohm would this yield proper operation?


Based on the above,  this should work. Be sure that your capacitor will have 10 uF or so minimum value over all operating conditions.