Properties of Satellite Chromosomes
If by "satellite chromosomes" you mean "satellite repeats", then:


Not always. There many types of satellites, such as telomeric, centromeric (like gamma, alpha, beta satellites), simple repeats (CT)n.   
It is still an open question. Some say they are important for chromosome structure (e.g., centromeres). Sometimes satellites get transcribed as might act as lncRNAs. And of course, most of them are just junk DNA.
If there is T then there is A too. 


Edit  


Satellites contain telomeric repeats at their ends as all chromosomes do. But they are more about NOR repeats.
They are important for the nucleolus functioning. But shorts arms of acrocentric chromosomes are not crucial, take Robertsonian translocation as an example.