Is there a required minimum impression purchases
No there isn't a set required limit you can purchases 1000 impressions if you would like. Example lets say the price is set at $6/1000 witch is $6.00 per thousand impressions you have the option to buy as many impressions as you would like in increments of 1000. The very minimum would be 1000 impressions witch would only cost you $6.00 to start your campaign.