Comentário oficial
There are no limits on the number of images you capture in any level of the app. You could do normal missions with the free tier and collect thousands of images.
You can use the Ground Offset feature to take off from a height that is above the ground.
https://support.dronesmadeeasy.com/hc/en-us/articles/209895406-Ground-Offset
If you want to do grid you have to have the Base tier. Sampling is only available for the Pro tier and also requires iOS and waypoint capable aircraft (not the Mini 2).