title_body: recommendations for a DIY/dev platform lifter drone
upvoted_answer: To answer your main question, I'm afraid there's nothing as widely used the Ender3.
  It sounds like you want to build something with more lifting capacity and space than a race quad, with GPS.
  There are two main styles of frame that might suit you.
  One is based on the old 'DJI Flamewheel', which has plastic arms attached to hub of two flat plates. You can build these with as many arms as you want but the arms are only available in one size.
  The other option is the many designs that use carbon fibre tubes. The tubes are very light and strong, and fairly cheap. Commercial designs use injection moulded or CNC aluminium fittings, but these would be perfect for 3d printing. Here's one I found but I'm sure there are others.
  Unlike a 3d printer, the mechanical design of a drone really isn't all that important. You could use bits of broom handle and plywood, and it would still fly. That's lead to a wide range of designs and no clear market leader.
  I'll have a go at the other questions:
  
  sorry, I don't know much about the options here.
  
  more blades is less efficient, which is probably why you can't find any multi-blade folding props. I'm not sure that more blades are quieter, unless you're comparing it to the same size 2-blade prop spinning faster.
  
  most people use Velcro straps, which are lighter than sliding mechanisms, and work with a wide range of battery sizes. Batteries need replacing every few years, and you can't guarantee getting the same exact size.
  
  the DJI video unit is the only real option for high quality digital video at the moment.
  
  
  This is different to the video used in quads like the Mavic, that transmit via wifi to a phone.
  Racers use much cheaper analogue gear based on old CCTV signals, but the picture quality is limited to old PAL/NTSC TV resolution. It's easy to send an analogue signal to a screen, and you can buy screens with built-in receivers. You can't always see screens in strong sunlight, which is why people use goggles.
  
  Systems that transmit to a phone are generally proprietary and only available as part of a complete drone. They also have a noticeable lag, due to the video compression/decompression required, and other processing on the phone. That's why they're preferred for taking video, but not for high-speed flying. At the moment you can't have both (although the DJI air unit is close).
  
  betaflight is the firmware run on race drones. It's not aimed at autonomous flight like the Pixhawk.
  
  No, because there's no common wifi module for drones.