Just realize that all carbohydrates are nothing more than glucose molecules bonded together to look like carbs. When those carbs hit the gut, they are changed directly to sugars that spike your blood glucose. Insulin rushes in to control the BG and any of the energy not used immediately is stored in the fat cells of your body.
Eating carbs has the same effect on the body as consuming sugar. So don't consume sugar. Yes, you are sabotaging your progress with any sugar or carbs.

To not store the energy in the cells of your body as fat...thus reduce your BF%...you have to fuel yourself with meat and fat. Butter, Palm Oil, Coconut oil, eggs, bacon, beef steak, lamb, chicken, the fattiest you can get, etc. The protein you get from the animal products is enough to sustain you. The problem becomes how to not run out of energy on zero carb...just eat more fat. Coconut oil has 120 cals per tablespoon.

See this previous question about running out of energy late in the day: http://paleohacks.com/questions/18974/why-am-i-hitting-a-massive-wall-in-the-afternoon-evening-after-dropping-sugar-dai#axzz1B3imtn4b

Zero carb eating while on a conditioning/muscle building program can be done. Carb loading is not necessary once you become a fat burning machine.

I like Charles Washington's blog http://blog.zeroinginonhealth.com/ He is an athlete who practices strict zero carb and performs very well. Look around his blog. He has been writing since 2008.

There is no set point of sugar or carbs for fat loss. Everyone's body is slightly different. I lost over 100lbs and I was eating 150/200 grams of carbs and whatever sugar I wanted. I dropped body fat and built muscle, but I had a lot to lose.

To try and answer your specific questions...

Many people on here agree that avoiding sugar leads to weight loss, (I understand individual results vary) but what should this target be? Would it be 0? say 25 g?

I would go by carbs rather than sugar, because that is what I am used to counting. I personally am in the 75/100 gram per day range. If I were working on fat loss I would drop them to under 50 grams.

Would this be higher on re-feed days if that was the method I was using to strip the bf?

When working on dropping body fat, I wouldn't have many refeed days, maybe one a week. On that day I would raise the carbs to 100 grams.

I've heard mercola say no fructose PWO as it affects GH (i think) but Martin over at leangains consumes a lot of fruit while maintaing very low bf%.

I think avoiding fructose while leaning out is more common. Martin is already extremely lean. It is easier to add things back in once your where you want to be.

Also, does it matter what type of sugar? i.e. sugar in Organic cottage cheese, or raw dairy? Should I avoid these, or not worry?

I would avoid dairy while working on leaning out. The type of sugar does matter. For leaning out preferred carbs/sugar are usually vegetables and sweet potatoes/yams.

you wont lose your abs under 100g of glucose if you are at all active. On heavy days, I sometimes exceed that amount.

I would avoid the fructose for optimal body weight if you want to stay CUT. Berries are very low fructose fruits, I eat them a couple times a week with no adverse effect.

I have had a few fructose binges that have made me both feel bad and require a cut period to recover from bloating hiding my abs.

my rule for sugar, glucose or otherwise, is Exercise BEFORE for optimal nutrient partitioning.

I think successful weight loss is dependent upon the extent to which an individual can first cut carbs down, and then convert those remaining carbs from sugars to starches.