I wouldn't build a 1.5L block. If you want to stay with a SOHC, at least find yourself a D16 block, cuz you'll have the longer piston stroke.

B-series is much more expensive to start with, but obviously you'll have greater potential for power later down the line. Keep in mind that, with a B16 or any other B-series engine, you have to upgrade your sway bars and springs to compensate for significantly increased body roll and nose dive. A B-series swap involves more than just the powertrain. Hence the added expense.