Everything that
@aquacat8 wrote. She's right on the money. The Channel Islands have some great diving, and it's not particularly hard diving, either.
Regarding your specific question about currents, I've never experienced strong currents at the Channel Islands. If there is a current running, the boat usually moors out of it, in a relatively sheltered location. That being said, there is sometimes a mild current; if so, you'll need to follow a few basic guidelines.
Basic Tip #1: Wear gloves. As you already know, California water is coolish, so thermal protection is a plus. Even more importantly, you're going to be holding onto well-worn synthetic ropes, so you need to protect your skin.
Basic Tip #2: Grab onto the anchor line. Hold onto it/let it slide through your hand as you descend and ascend. Doing so will (a) keep you together with your leader/buddies, and (b) ensure that you don't go floating off during your safety stop.
Basic Tip #3: Use float lines to drag yourself on the surface. Once you giant-stride into the water, use the bow-to-stern rope and drag yourself forward to the anchor line. Once you surface, float to the stern, grab the "granny line" trailing off it, and wait your turn to get aboard. You'll expend less energy and save your breathing gas.
A bigger issue is surge. You might find yourself being pushed back and forth by the wave action. Don't fight it. Just (literally) go with the flow. As long as you're not next to a reef, it's all good. You can actually swim through the kelp forests very easily, as the stalks are swaying back and forth.
Thinking of kelp, here are two tips:
- Eliminate all the danglies from your gear. They're kelp-magnets.
- Kelp is extremely strong lengthwise, but it's weak crosswise. In the unlikely case that you get seriously tangled, bend the stalk and it'll snap.
Have a good time!