Master card world elite has unlimited lounge access on credit card unlike visa version which has 6 access per quarter. However priority pass issued with both the version has unlimited lounge access.
2nd card bhi le sakte hain. Aap technofino ka YouTube video dekh lo. Mere pass bank se call aaya tha 2nd card apply karne ke liye. Maine customer care ko mail kiya tha , unhone review kiya account ko and Branch ko bola mera physical application lene ke liye.
2nd credit card from Hdfc is possible but it has to be applied through branch. Your existing card is on visa/master platform so you will get 2nd card on diners platform. You can keep minimum floor limit of existing card and rest of the limit on 2nd card.
As per rule , you can not take anyone on your card . But if you have multiple cards with lounge access facilities then you can take in domestic lounges. I did many times in Bangalore, Delhi , Hyderabad and Bombay.