Server/SCSI raid 1 question

hello,

im going to be building my own server soon and i have never done it. i currently have a NAS 2TB in raid 1 that i use for media and it works well, but i am running out of space in the near future. I would like to build a server using SCSI/SATA/SAS or other type of storage that would help me in; 1. having more storage in raid 1 and 2. being able to increase storage when i have the money. im looking into getting a X24 3.5mm bay server chassis, putting in a MB and have X4 2TB hard drives and raid 1 then into 1 logical drive of 4TB. my questions are;

1. should i use SCSI controller so i can have 8 - 12 drives per line?
2. im unfamiliar with SCSI controllers, do i need 2 for a total of 24 drives, or do each come with 2 lines?
3. do i need drives on both line to be even for raid 1? or can 1 controller have 12 on it raided 1?
4. when i get more drives, if i add 2, will it reformat the index platters of the already established raid or will it just add the space onto the end of the logical drive?
5. do the M's for servers come with the ports that i need for 24 drives already or do i need controllers?
6. if one day i have all 24bays and the server at max, can i have another one like it and make both servers into 1 logical drive?
7. i want to use linux as my OS, would this be a good OS for streaming media and the server?

any information or links of web pages would be most helpful.

thank you!!!