I agree with Yooper: I think it was fine to transfer when you did and I think your beer is totally fine right now. You're not seeing a lot of activity in the beer now because it sounds like it's almost done fermenting. Beer usually has a really active fermentation in the first few days and then tapers off after week. You'll see activity if you add sugar water at this point, but that's just the yeast eating the sugar water -- not actually any fermentation in the beer itself.
Re: shooting CO2 into the carboy -- I wouldn't worry too much about it. If you've been seeing ANY bubbles in the airlock, that means that there has been enough fermentation that CO2 is pushing oxygen out. (CO2 is heavier than oxygen, so it will create a barrier over the surface of the beer.) Also, much of the point of transferring beer into a carboy is to reduce the surface area that ultimately gets exposed to oxygen. If there's a little in there now, it really don't think it will hurt your beer (I've been brewing for years, often see no fermentation activity in the secondary, and haven't had oxygen off-flavors yet)
Re: putting the used yeast sludge back into the secondary -- don't bother with that either. The sludge is just the spent and dormant yeast that's fallen to the bottom; there's still active yeast buzzing around in the brew itself (that's why beer carbonates when you add a bit of sugar during bottling -- the yeast still in the beer get a kickstart!)
Hope that helps! Good luck with the ale!