Yes, you can use Blue Lace tape anywhere on lace. If you use at the front hairline, it can show through the lace a bit if your density is on the low side, but I'd still use it for swimming for the safest bond. You can always style your hair down a little in the front to hide the edge a bit.
If you have any poly areas on your base it's better to first put down a layer of Red Liner tape on those areas, then put another layer of Blue Lace tape over that. The Red Liner is much easier to remove from poly.
Here's a link to a good video showing how to do it...
http://www.youtube.com/watch?v=lU5sJW0SDkI
This video shows a perimeter attachment, but as I said earlier, since you're going into the ocean you'll want the best/safest bond you can get, so I'd highly recommend some extra strips of Blue Lace tape across the top and center of your unit for extra hold too.
The best place to buy supplies is from hairdirect.com. They have the best and most comprehensive selection of products for hair systems. They carry several good brands of leave-in conditioner with sunscreen. A good one I've used before and like is PPI Enhance. They also have a great video library section that you should watch when you get a chance that covers all the steps involved in wearing and maintaining hair systems.