Oracle DB backup questions

Hi All,

Sorry if I asked more questions below, please help to understand this.

1. I have 2 ora databases in one server, have different SID and TNS.
The backup for DB1 with SID1 in rman script is completed succesfully, when I browse backup, I can see all datafiles for DB1 and DB2
Does it mean rman backup both DB1 and DB2?

2. For DB restoration (datafiles, tablespace, arclog), do I just follow restore wizard in client gui, like doing FS restore?
Or I have to create rman restore script?

3. If I enabled compress in policy, any impact of this? pros and cons?

Thanks Alot