It sounds like you've gotten quite a few things mixed up here. Here is how you should be using the 13 Herb Bath:
1. Yes, the candles are important, but not everyone lights candles when they do a spiritual bath. I recommend them for the 13 Herb Bath though, if you have them. You place them on the side of the bathtub (or on the floor if you have a shower stall) so when you step out of the bathtub, you step in between the candles. You can read more about this ritual here, under "Leaving the Bath":http://www.luckymojo.com/baths.html
2. A lot of your other questions can be answered if you carefully read the instructions that come with the herbs:http://herb-magic.com/13herb-bath-13.html
The instructions specifically say to let the herbs steep for 13 minutes, and you do strain out the herbs before using the liquid.
And your latter instructions are more on the mark, FYI: This is not a sit down and soak type of bath. I'd recommend putting your prepared herb tea into one big bowl and bringing that into the bathtub with you, as well as a cup. Use the cup to scoop up the water and pour it over your head 13 times, praying the appropriate Psalm and rubbing downward. As you pour, just put one of your feet into the bowl, and that will guide some of the water back into the bowl, getting your "essence" into it. As you bathe, just be mindful to leave a little water in the bottom of the bowl, and that's the water you take to the crossroads.
Hope that helps!
Thank you, St. Michael, St. Expedite and La Santisima Muerte!