How to change the style of the pages title in a view? I've created a content type view using teasers. The titles are all H1s. How to change that to H3, for example?

Is this just a case of CCS?
Open firebug to see what are the ancestors of the h1, there should be a name that contains the content type or view, you can easily set:

.WRAPPER-OF-CONTENT-TYPE h1{
    //here is your css style
}