I am amazed how simple people imagine the process of developing good 3D models to be. With the mentioned methods you are lightyears away from ever getting something useable!
1. You definitely do need an autonomously flying system as nobody is able to remote control a UAV from the ground precise enough to make pictures in equal distances from each other along a STRAIGHT line (not to mention many parallel lines, including constant overlapping in both dimensions). So: forget it!
2. Besides that, it is pretty challenging to develop software that is able to control the UAV in such a way that it flies along lines with a horizontal and vertical deviation less than 2 (vertically 5) meters, including compensation for wind and turbulence. If you cannot, there will constantly be holes in the pattern, as well as too much and too little overlapping to get good 3D data. It took us quite a while to handle this problem.
3. You need a microcontroller on board that is able to release the camera shutter depending on the UAVs position. Otherwise wind will have a great influence on the stability of the picture overlapping factor, which again destroys the 3D data quality. The controller needs environmental data like true airspeed, wind component and so on. Besides, the camera has to be able to fire quick enough. The alternative to set the camery in continuous fireing mode, shooting 2-10 pics per second, won't make you happy as well, as you will get a mountain of pictures which certainly will bring your PC and Photoscan down to its knees.
4. Think of the required payload! The UAV has to be able to carry at least 400 g payload. The mentioned toys are miles away from providing it.
5. You need mission planning software, data about the optical and other performance factors of your camera and lens and have to match it with other control factors of the plane and hardware.
6. It is more than helpful to have a bidirectional data link between UAV and ground station.
7. Be sure: the law is you very smallest problem! In Austria it is - like so often here - not really forbidden, but also not completely allowed. Anyway, they are going to adapt it currently.
8. I don't see how a pilot or a second person on a "real" plane could be able to make pictures which obey all these required conditions. You will always have parts of the plane on your pictures, which alone can drive you crazy when putting the pics into PS. Not to talk about how hard or - in fact - impossible it is to fly along straight lines with minimum deviation without some special instruments. I know what I am talking about, I am holding an airline pilots license.
9. - 30. .............
With other words: much better you tell an expert what you need, pay him some money and get a very high quality result. Even more, as you seem to have more money than is necessary. :-)
Greetings
Oliver