Stand with your feet at about shoulder width, arms out to the side, fingers slightly facing upwards, relax as much as possible and take a deep abdominal breath, but use your abdominal muscles to keep your stomach from expanding (i.e. reverse breathing). If you can feel something pulling in your finger (perhaps also hands, forearms, etc.) beneath your skin, that's the suit.
If you get a headache, you're trying to hard. Thinking of pushing down with the diaphragm helps me to keep the pressure from rising to my head. (So a big
warning here: be very gentle with yourself, overdoing this will lead to medical problems related to high blood pressure. Proceed at your own risk.)
Hmm... not how I would phrase it. The suit with the tanden as center as certain physical properties. If you exert force on it, the force will follow certain lines through it, because of its physical properties. That's where the idea of the meridians probably comes from. My intended training progression is: suit - lines - tanden. (With plenty of overlap, of course. First develop suit until aware of the lines, then allow one to inform the training of the other, etc.)
What kinds of grabs are you thinking of?
The standing practice of Taikiken (aka 'ritsuzen', 'zhan zhuang' in Chinese) has helped me in developing some 'suit', but the more breathing practice I do, the more obvious it becomes how useful it is. I have the impression (don't think it's entirely correct, though) that standing works more from the outside in and breathing from the inside out. Anyhow, good breathing practice will pressurize the abdomen, so if you want to train the hara, it makes sense to do something that works that area, no?