Could not fit in a comment...
This post (and the excellent answer from Richard Smith-Unna) lists the species that have the smallest genome that we are aware of in different clades.
Yes we can/could sequence these tiny genomes and try to understand what each sequence does. I think that to understand the minimum requirements for life you will mostly be interested in theoretical cytology and synthetic biology than in sequencing simple genomes.
Note that the basic requirement really depends on how you define life. Is a virus alive although it has no metabolism? Would a self-replicating RNA be a living thing? Because we were able to artificially synthesize self-replicating RNA. While the subject is interesting, the main issue is a purely philosophical one: How do you define life?