In reference to your question as to whether a flash adapter for a C330 works TTL and you need a particular flash to do so, I don't know. That might be referenced at the Mamiya site if you care to look. Regardless, and I'm sure you must have x synch, instead of looking for a low power flash that would work for the way you want to shoot, instead look for a powerful flash that is manually adjustable. You want something that can mimick a studio strobe where you can set the power (flash ratio in small portable flash terms) at what you need. This way you can use it for a variety of uses, background, hair light etc and have the power to do so. Also you'll want to diffuse the light with silk or other diffussion material for softer light when you want it, so you'll need something with more power. There are so many models available so that it's really up to you in what you want to spend. Personally I use Nikon SB24's, Sunpak 120 J's and recently bought a Metz 20BC, althought it's not manually adjustable, except for me moving it back or forth. Any flash will work, and manual is the way to go for sitting portraits.