1)In the modern army, you must have completed the minimum mandatory service requirement of 12 months. Then you can volunteer for the spetsnaz preliminary course, which lasts 2 weeks. These courses are held four times a year. In this preliminary course, you are subjected to mostly physical tests. Then a team of veterans give you points. These correspond to stars, five in all. You must have achieved atleast four to progress to the main course, the brutal six months of hell.
2)The ranks of the spetsnaz are the same the respective branch. For example, the naval units have navy ranks while army units have army ranks.
3)I'm not sure what you mean by power and strength. But if you mean firepower available, I day Spetsnaz are superior because we have lots of support available except on covert missions, and even then individual troopers carry lots of equipment on themselves.
4) Spetsnaz are specially trained for unconventional weapons and tactics. And at the same time, they are experts in conventional warfare. Regular army units rely on tanks, IFVs, APCs, aircraft, artillery,etc... They rely on unit cohesion and numbers. Spetsnaz are trained to fight as individuals, then when these individuals are put in a sqaud, they become even more lethal.
5)If by any chance you are considering trying out for the Spetsnaz, (which doesn't seem likely at all) you should start out with a physical training regime unheard of in other countries. Try doing 500 pushups a day, or 300 crunches, or finishing a 3km course in 12 mins carrying 30+kg of equipment.