Generally I don't adjust my water amount, but I also don't soap at "full water" either. I usually use a lye solution concentration of 30% to 33%.
If you use a "full water" setting (aka the 38% "water as % of oils" setting on SoapCalc) for your soap recipes and are adding quite a bit of liquid color, fragrance, or whatever, you may indeed want to reduce the amount of water a bit. Here are three reasons why:
Any time the overall percentage of water-type liquids causes the lye solution concentration to drop below about 28% (this is not "water as % of oils" -- I really mean "lye concentration" here), there is more tendency for the soap to separate in the mold and make a huge mess and icky soap. If you're trying to avoid gelling the soap, increasing the water content will work against this goal -- more water in the soap means a lower temperature at which the soap will gel. And finally, more water means the soap will be softer after saponification is over, all other things being equal, and that may prevent you from unmolding and cutting the soap quite as soon as you might like.
I don't. I sometimes mix my colors with a small amount of water (1 tablespoon or so). It's not enough to make a difference. If you are worried about it, you could reduce the water in your recipe a bit.
Fragrance - are you asking about mixing your fragrances with water before adding? I don't know if anyone who does that. I will sometimes add my FO to a tablespoon or so of olive oil before I blend it in the soap batter. That can help to slow down seizing if your FO is prone to that. Again, it's not enough to worry about.