So this was the thread I was looking for! I hope people are still following it...
I'd like to make a fruit beer but my big question was whether you need to compensate the sugar you add when using fruit or do you just add the normal amount and the fruit?
I also didn't know you want to let it sit so long. Basically the gist I'm getting is to do my primary then rack it to the secondary where I have my fruit concoction (5 lbs of fruit with very hot water poured on it and then mashed) and then let that sit for a longer period of time. Am I on the right path? It will be my third batch of beer.
Fruit, unless it is something like a wine grape, generally doesn't contain a heck of a lot of sugar (by weight). Of course, some fruits contain a lot more sugar than others. There are sites out there that list the % by weight of sugar in various fruits and you can go from there. Adding 5 lbs to a 5 gallon batch wouldn't require much, if any, modification to your original recipe unless you are trying to keep the abv below a certain threshold or it were a very high sugar content fruit.
I've found that fruits can be tricky. A batch of wheat on raspberries may be totally different in time to glass than the same batch on strawberries. The varibles go up exponentially when adding fruit to a recipe as the fruit may take days, weeks, or even months to mellow, meld, etc. with the beer, and, of course, the type of beer involved will be a major player in how long the process takes. Plus, your individual tastes may come into play. Fruit tends to mellow over time. So, if you want a fruity kick, you'll probably want to drink it eariler than if you want notes of the fruit blended with the beer.
You don't have to mash your fruit in secondary or even heat it but this is highly dependent on what fruit you have and where you got it. If you're working with blackberris you hand picked, you'll probably want to take more precautions than you would if you were working with pre-frozen blueberries or pre-pasteurized, canned pie cherries. Also, if you've got something like a raspberry, you don't have to do a lot of mashing and heating as this will release pectin and may cloud your beer but something like a plum may require some mashing to get at the pulp (and all the good flavors). Also, freezing helps this "pulping" in all fruit and is generally recommended as this will help break the cell walls within the fruit and allow more of the good stuff to get out.
You've got the gist down pretty much. Basically, I brew and ferment a beer as usual, get the fruit ready by the means above and put it into a secondary container, rack the beer on top of it and just let that ferment. This can take a few days to a few weeks. A lot of fruits will turn pale and fall out of the beer but others will just hang out on top and float. I've found I am able to bottle from this point but some will rack a third time and allow the beer to clear without the fruit before bottling. And like I said earlier, it may be ready to drink in a couple of weeks or it may be a mess, it really depends on the fruit and original beer recipe.
In the end, these are just my experiences and what I've learned. Others may tell you differently and that's the joy of this hobby. Everyone can do things entirely differently and we all wind up with good beer!