A good resource about this is the things network. You might not use it but they provide much information that is usable if you don't want to look up the LoRaWAN datasheet.
As for bandwidth:
Compared to a higher spreading factor, a lower spreading factor provides a higher bit rate for a fixed bandwidth and coding rate. For example, SF7 provides a higher bit rate than SF12.
Doubling the bandwidth also doubles the bit rate for a fixed spreading factor and coding rate. Spreading Factor | Bandwidth | Bit rate (kbits/s)
7 125 5.5
7 250 10.9
7 500 21.9
AFAIK: bandwidths are fixed for LoRaWAN depending on region and usage. Europe (868MHz) mostly uses 125. USA (902MHz) seems to use a mix of 125/500.
The increase of the datarate can impact the resilience of your transmitted data. If your bit is 1s long instead of 1ms it is far tougher to interference. An increase in bandwidth can also strengthen your transmission as more needs to be interfered with for the transmission to be unusable.