Whether or not you should add more yeast depends on how long you've had it fermenting and lagering, but as a rule, if it's been less than three or four months, there should be enough viable yeast for you to bottle condition with.
I would also recommend using less sugar, no more than 5oz and probably less. Even with a 'lively' lager such as a Pilsner, you generally don't want more than 2.7 volumes of CO2 in the finished beer, and unless your temperatures are absurdly high, 6 oz. will give you closer to 3.5 or even 4 volumes. While that shouldn't be enough to cause bottle bombs, I think, it could lead to fobbing; the last thing you want is for most of the beer to rush out in a fountain of foam as soon as you open the bottle.
BeerSmith has a nice tool for estimating the amount of priming sugar you need, and I expect ProMash and other programs do as well; if you prefer to do it by hand, you can use the nomograph from How to Brew to estimate the amount you want.
Mind you, I'm not one to talk, as I consistently used 5oz. for several batches (it was, conveniently, the amount the stores had pre-packaged for priming sugar), and as a result got beers that were over-carbonated for their styles. Live and learn.