DJI products have been the best out-of-the-box solutions for instant aerial video commercial applications, for the last few years. This is certainly a valid way to approach obtaining aerial footage. DJI products, like the inspire, create very affordable aerial video at a very affordable cost.
Inspire is an excellent product, however it constitutes a serious risk for those who are not experienced in flying UAVs. Although these machines allow you to observe what the camera is taking while in flight, they are designed to be flown line-of-sight LOS and not FPV.
The reason for this is simple, the camera view can be confusing as a piloting perspective. The orientation of the camera is independent of the orientation of the aircraft. With LOS , the pilot understands the orientation while a separate camera operator can aim the camera. Alternatively the pilot camera can aim the camera using a tablet on their Tx.
While this sounds very flash, it has drawbacks. LOS is limited to a few hundred meters, while FPV has a thousand meters or more. 3D gimbals have greater freedom but are not so easy or necessary when filming from the air, especially when the pilot is also the camera operator. I prefer 2D gimbals because I can use the drones yaw to rotate the camera and the aircraft.
The camera used with your drone can be a large as the UAV can carry. That doesn’t mean you can go to a load where, full throttle is needed to hover. This will end in disaster and has. The GoPro is often the camera of choice because of it weight/quality ratio. To increase the camera weight means an exponential increase in the cost of the aircraft. More motor/props and larger propellers are only the start. Batteries need to be much larger and very much more expensive. Carbon fiber frames are a necessity if you wish to use larger camera gear. The gimbal will need to larger and hence heavier. All this adds up to big dollars with dubious improvement in image quality.
Zoom lenses are and big weight burden. They are also a control issue that needs serious complexity for radio communication. The aircraft has the ability to move close the almost anything, so its hard to justify the addition of large zoom lenses. DJI have put significant time into creating small camera with suitably small zoom lenses. Their efforts are not to be under rated as is makes sense to go small with this stuff.
Custom solutions are not common in the aerial video business because it takes away from your core purpose, to take video or photos. Time spent perfecting an aircraft that can be purchased off the shelf, is time that your competitors are using selling their imagery. So why would you do this? Because you can have the freedom to repair and modify your own UAVs. Fixing damaged or faulty gear is not easy if you have little idea how it works. The best solution is usually two people, so you can divide the learning time and get both boxes filled. You need to take images and get them out there and you need to be able to work on you own gear.
Custom solutions are sometimes required but you really need a team. Most UAV projects are not really custom but kit projects that are unreliable and risky to use. If you have a team where one or more people do the design and construction, while others work on imaging and others promote, you can go this route. Custom imaging UAVs are a big deal and not the first choice of you wish to make a business of this fledgling industry.