You want to make sure that the connection to the site is safe, the database is secured and the site is accessible only to people with privileges. Btw. It doesn't matter where the clients are. Anything but an in-house connection requires the same security measure, no matter the distance. There are several ways to do this: If you can setup a virtual private network with all your clients, that's the safest. If that's not feasible because your clients are more short-term clients or individuals (rather than long-term company contact) then it's more complicated. A lot also depends on the number of clients you are wanting to handle. You should definitely talk to a security and privacy expert and then you probably need to hire a system administrator that is able to maintain your site with updates and keep it secure. You probably also want to talk to a lawyer to keep you safe from lawsuits by defining the terms of services of your website in the right way and to also estimate the potential damages that could happen if things go wrong, so you can prioritize. I can offer advise on the technical side of things so you can take it from there once I know your situation a bit better.

It varies and it's very very specific to what you want to develop. The concrete design of your circuit matters. Also prototype building costs are usually a factor 10-100 higher than series. If you already have your prototype then you can shop around various manufacturing companies. To do that, you need Gerber files (your PCB design) and a bill of materials. You also need to think about casing: designing it and creating the mold is expensive. If you don't have your prototype yet, I recommend having it engineered in eastern Europe. Custom engineering is cheap there and high quality. IP protection is a problem. One thing to do is to distribute the work to different manufacturers. For the design phase you are safer if you design your prototype in Europe or the US where international patent laws apply. I could give you more specific advise in a phone call, getting to know a bit better what you are trying to build.

It's hard to get a definite answer to this as these companies will not tell us how their algorithms work. Having said that: Based on my experience working with these APIs, it is totally possible to implement a real-time search like "socialmention.com" purely based on the APIs from Google, Twitter, Yahoo, or Facebook. On the other hand, crawling and saving all that data just for the eventuality that a customer might search for it is probably not economically viable and will also violate the Terms of Services of most of these APIs. Bottom line is: They are probably not crawling and caching.