Hi Tim,
I am sort of in the same boat. Laravel is the most popular PHP framework currently, which I am sure you are aware of. However, IMHO, it is rather opinionated. But, as a quick start basis, it is probably the best choice. Most devs like its ease of use and lower learning curve. I personally like Symfony better. Only because I feel it is one or two steps more professional than Laravel. Not from a programming quality standpoint, but from a directional and “leadership” standpoint. Did you know Laravel is built off of a considerable number of Symfony components? So, the decisions Symfony makes affect Laravel too, in some ways.
The question “what should my application do” is what you should mainly concentrate on. If you can get adept programmers to work with you (a problem I have with my startup) or if you have the means to hire them (also a problem with my startup), then let them figure out the technical side of solving what your application should do. The fact you’ve already decided to go with PHP is an important directional decision, tbh. I think it is a great decision. PHP is a great platform for web application building and although Facebook has come up with their own version, you can see you can go places with it. That being said, the type of applications you mentioned are very client based. You’ll need some very good frontend devs.
Make sure your ideas are down on paper (or any other medium to read from) and well described. Documentation is key. Let people in on your idea. I have been writing notes down for ages, however, I know that 95% of the people that see my idea go “I don’t get it”. That is either extremely good, because it means it is completely unique, or it is extremely bad, because I can’t communicate my ideas properly. I feel, because it isn’t 100% that don’t understand, then I know it is the former, my idea is very unique. 
At any rate, my best tip is, if you can’t program yourself, stick to describing the idea by all means possible and let your team solve the technical challenges and details. I believe that is a winning combination.
Scott