Don't go messing with your ph.. it'll only cause problems for your fish.
Your plants will adjust in time. Or .. not. :D Give it a few months, see if they improve.
When you get your wood, boil the crud out of it for a couple of hours (some people do this for days, I feel this is a bit of overkill, really) to remove any wood gunk. Then soak it in a bucket until it'll sink.
You'll probably notice your water turning yellowish after you add it, but that's just the tannins in the water leaching out of the wood. Bettas evolved in 'dark water' like that so your fishy will probably really like it. It's not harmful at all and will fade after a couple of months of water changes.
Sometimes it'll get a kind of white goop on it. This is why I keep shrimp.. however, it'll die off on its accord after a week or two, you can just rinse it off in old tank water or suction it off with a vac.