Don't most "tame" yeast strains give off most aromatics during fermentation?
You are correct that most esters and other flavor chemicals are produced during fermentation. In my experience this is much more the case for Sacc strains and not Brett strains. Beers with Brett will change considerably over time with no change in gravity.
Since the gravity of this beer is at 1006, can I expect much more without additional feeding (ie. fruit or sugar)??
Yes, the flavor will change significantly and more than likely toward the funky side and not fruit side. There is a cycle to how the flavors work. The beer will continuously go through a esterification cycle. I am not totally sure about the science behind it but know it works through experience. You may like the taste in 3 months but not 6 months and then like it again in 9 months. This is the reason that you see patience preached so much on this forum.
The flavor right now is just ok, but not as fruity as I expected. Maybe Brett c was too mellow of a choice?
Well, if fruity is something you wanted maybe a Sacc + Brett yeast blend would work better.
And if you want a Brett strain that will give you more "fruit". The Drie (Avery 15) Brett strains gives off some great tropical fruit flavors.
I'm not sure you best way to get this strain but, one option is to ask Chad at Crooked Stave. And his beers are bottle conditioned so you maybe able to get some fruity Brett strains that way. His pure guava petite sour gets the guava flavor from the Brett strains he uses.
Since I took a sample, should I purge the head space with co2?
It really depends on the amount of head space you have. I have not had a problem with acetic acid and I never purge the headspace. But I only taste every 3 months and I use 5 gals in 5 gal Better Bottle.