Q1: Look in the datasheet page 3 , under Rated Load, I see at least 2A @ 250Vac , so you can switch mains voltages (be carefull)
Q2: many transistors for your type of usage (LED switch) will be fine , BC547 , 2N2222
- Make sure its a NPN
- A 100k resistor in the base is fine.
- Emittor connected to GND.
One note : For switching the LED like in your schematics the BC547 is fine, It can handle the current of the LED,
But if your want to switch a relay with this BC547 you have to watch out, a (NON)-Latching relay coil requires more than 100mA and the BC547 is only rated to 100mA.
It is unclear to me what the rated voltage of your relay is , when in doubt use a 2N2222 it can take 800mA,