For coin farming, and for getting the 2x red brick...
As stated, go to the LOTR world with Gandalf, hop in the Batmobile and chase down the red brick. You'll have to purchase it at the main portal in the home world (I had a hard time figuring that out because I put the game down for a few months, so if you forget, that's where you have to go to upgrade.
My one change is how to grind the million coins to buy the brick. Go to the DC world with Batman, but stay in the car and blow up every car you see. Shooting the cars with the Batmobile really helps so that the cars give coins by the time you get there (less time circling).
Cars this way seem to give a boatload more coins this way. There are a lot just in the level. Make sure to use the jump pad to get in the parking garage, and go to the parking lot by the cathedral. Then go to the asylum, down the stairs, and use the Batmobile again to blow up all of the beds, cells and everything in the back. When you're done, go back to the hub world and repeat.
I got about 100k-200k or so each time. Your mileage may vary, but the stud were absolutely flying in every time I blew up a car.