1. As in any language,
2. As in any interpreted language. Yes PHP has the gag operator (@) but it's use is discouraged (and not used in this example),
3. Not in my opinion. The Symfony framework alone has a ton of well used packages[0]. It does look like someone's decided to build their own framework from this example though,
4. Opinion.
Scheme, Standard ML, very early versions of Java, and BASIC come to mind.
Static typing really does seem particularly important in this domain, to the point that if an engineer is unable to find a suitable interpreted static language then the prudent choice would be to start looking at compiled langauges before relaxing the static typing requirement. Even implicit type conversion seems like a pretty questionable idea in this sphere. You really would want to be keenly aware of when you're doing something that might add or remove numerical precision.