First Lense for my GH3

I've gone back and forth from the BMCC, Mark III or the GH3 and I'm pretty set on the GH3 for its reception, my lack of experience and it's price. Now i need to know what to get with it. Obviously i need my first lense as well. Whats a good one to start with for someone that will primarily be shooting natural and structural objects with the long term cool being Documentary/Cinema shooting. Im tempted to spend the extra dime and get the Voigtlander but part of me tells me I dont need that yet. Instead i should go with a Sigma 19mm or 30mm (which would i need or do i need both?) Any suggestions for a novice like myself? Thaks guys you've been a huge help