Tweaking this BIAB recipie

Well, im gonna try making a 5 gallon batch of Lager. Ive only done kit beers before.

So this is what im wondering abouth. Im wondering of thees malts would be a good match and how much would i need of them?

Pale Malt
Pilsner malt "Heidelberg"
Vienna Malt

Im thinking of using saaz hops for aroma and Northern Brewer pellets for bittering.

please give me a feedback on how this would work?

* been using http://www.hopandgrain.com/~alcoholcalculator.aspx to get an approx on how much grain and hops i would need for the right OG and IBU

If those are the three you have, I would go with a mix of mostly Pilsner and some vienna malt, maybe up to half. I think NB makes a great bittering hop and a saaz will be nice in a light lager. I think you're definitely on the right track.