I've never tried brewing with strawberries, but from what I've heard they are one of the harder fruits to use in beer. The problem is that strawberries are very sweet, but when you ferment them, the sugar all gets turned to alcohol, so you're left with a very sour, acidic flavor that doesn't really taste like strawberries at all!
This is why fruit beer more often uses sour fruits (raspberries, cherries) which will still taste recognizably like themselves even after the sugar is gone.
I'm totally guessing here, but it seems to me that to get a strawberry flavor you will need to keep the final beer quite sweet, but not a malty style sweetness. You could get that by sterilizing the beer after it has finished fermenting, then adding regular sugar, or (more easily and safer as they will be no risk of bottle bombs if you fail to sterilize 100%) just add some kind of non-fermentable artificial sweetener (a common technique in Belgium when blending lambic style brews).
I would guess maybe 4 or 5 pounds of strawberries for a 5 gallon batch? I would freeze them (to break down the cell walls) then add to the secondary fermenter once primary fermentation is finished (so there will already be some alcohol to protect against any bacteria in the fruit). This will kick of a secondary fermentation: wait until this dies down, then bottle, adding sweetener to taste.
