Sim in Bangalore ? Guys here prefer Airtel and BSNL usually.
As for Rajajinagar, I used to attend classes there. And I still visit the area often, around 4 days a week. Its obvious I know the place well.
I have no idea honestly about PG there, but yes, when you can rent a 3 bedroom house for under 15K per month, I doubt you will have difficulty in finding PG for under 5K.
As for food, I had the same issue when I migrated from Ahmedabad, but bangalore food is AWSSOME. The best compared to any other place, north or south. Its just perfect.