Traditional trams, rather than the modern Metro-style, appear to have had about 8 stops per route mile - based on what I have read recently. That is, about 220 yards/one furlong apart.
There would be no such thing as an average route length - it depended on the size of the city and how far into the suburbs the trams went. In Norwich, for example, a cross-city route might have been about five miles - but they were withdrawn in 1935 so I have only a vague memory of them plus a lot of reading.
Ray