Flashing MAIN+FS+Custom Will Debrand Your Phone. It Wont Unlock. To Unlock, You Should Use Remove SIM-lock patch generator - Top Sony Forums But Do This After Debranding. Since You Are New To All This Therefore Read General Information about Patch-Unlocking (start here if you want to unlock) - Top Sony Forums Before Strating Over. Since You Are In India, So Heres A MAIN+FS+Custom Combination For You.
MAIN: Downloads - R8BE001_RED52 - W580_R8BE001_MAIN_GENERIC_LA_RED52 - Top Sony Forums
FS: Downloads - R8BE001_RED52 - W580_R8BE001_FS_S_ASIA_LEVAN_RED52 - Top Sony Forums
Custom: Downloads - w580custpack - HB1-06_Gen_CDA102568_110_R8A_GENERIC_S_ASIA_LEVAN - Top Sony Forums
Since Your W580 Is Not In Dropdown List, So Use The 'Uploading Files Via FSX' To Unpack The Contents Of Custom Archive To "/tpa/preset/custom". For Your Last Question, NO. You Cant Download Firmware From Another Phone. Download Them From Download Area But Read This Before: How to get access to Download Area? - Top Sony Forums