How long should I try out any individual ad on a blog before I pull it if it's not ROI positive? 2 weeks? 4 weeks? 8 weeks?
Totally depends on traffic/impressions/clicks. You need enough data to get to statistical relevance. One site might get you enough data in a week. One will take you a month. The longer you run it, the more accurate your data is going to be.
How much should I try niche blogs vs facebook ads?
Pick one traffic source and master it, before trying to do any others. Both of those can make you money. Pick one and test test test.
What percentage of my revenue should I put into advertising while in launch phase? 20% 50%? 60%?
As much as you can afford, you're not going to get sales until you can figure out how to get traffic. If you get a positive ROI, and your ads are generating profit... then you have unlimited money for ads, and rocket that traffic source as high as it will go.
Favorite retargeting engine?
I've only done Adwors... it's pretty powerful.
In case it's helpful, my product is full-cost $89 with a 2.5% COGS and $39 of monthly overhead.
Those are some ridiculous margins. Is this an info product?