The Son'a seem to have no unusual characteristics for humanoids. Having originated from the Ba'ku planet, many are extremely old, having benefited from the rejuvenating effects of the metaphasic radiation while living there. Leaving the planet caused them to start aging normally, so they have used advanced medical technology to sustain themselves. They appear to have been one of the suppliers of Ketracel-white for the Dominion's forces in the Alpha Quadrant. A deal to stop them making this product may have been a factor in the Federation approving the Son'a's harvesting of the rings on the Ba'ku's planet.
The number of Son'a isn't known: those present on the So'na warships during ST:I may represent the entire So'na population. Their ship crews include non-Son'a races, with the Son'a being clearly in full charge. As such, their organization would be a military dictatorship.
The Son'a have access to technology comparable to that of the Federation, but there appear to be only a handful of Son'a. Their entire fleet apparently consisted of three warships. This would make them a minor power by most standards.