Here in western Oregon, we are heavy clay. The heavier the clay, the more helpful the char seems to be. I did a small hugel-char bed here. Haven't been very attentive to it, and it's only about a foot high. In the trench I put burnt wood. There are irises, oregano, thyme and comfrey planted in it. It didn't get any water through about a month of the summer, and things by then did look a bit dry. It is currently getting sort of starvation rations of water. I stand there for about 3 minutes with the hose on full blast -- not very impressive pressure -- twice a week. Everything but the comfrey looks good. The comfrey is getting eaten by something with 4 legs and fur, or wings and feathers, I suspect.
I think the charred wood I got from a clearcut slash pile. A non-technical way to find out if the char is reasonable quality is by washing your hands after handling it. If the black comes off pretty easily, there isn't much tar. That's the good stuff.
Plain char, smaller and completely burned is good too. I like a mix of sizes of char for mixing in the soil, I make my own (150 gallons this year and used 2/3 of it), and mostly it's 1 inch diameter or so. I may want to sift/grind a little for beds that might grow carrots.
I'm not sure how much to steep the char, don't put it with dry manure; expect it to absorb some moisture. I have a friend who gets char from slash burns and puts it in a barrel with whatever: chicken poop, dead fish, urine and a bunch of water. She pulls it out when she is planting.
I'm a lazy bum, and I just lay mine on top of the ground, mulch over it and let the bacteria colonize it.
If you put it IN the ground, definitely charge it. Haven't seen any issues with my method.
Try it, you'll like it!