MC - 757 wake
Morning
By ICAO definition (based on weight alone) a 757 is a medium vortex a/c and hence from a minimum of 3 miles (terminal control) and 5 miles (en route) would be needed.
However the actual vortex created by a 757 (and DC8, 707, VC10 and IL62s) is higher than the a/c weight would normally produce. Therefore, for approach spacing it is classed as an 'upper-medium', generally giving an extra mile over standard medium requirements.
Hope this helps.
PS. This only applies to the UK as I understand it
Regarding the other points, as a TC controller you have to be aware of vorex requirements although the only legal requirement that increases our 3 mile minimum is when an a/c other than a heavy is passing behind or in trail of a heavy. Then we need 5. Personally I always er on the side of caution and if a light is passing 4 or 5 miles behind anything bigger (and I get a spare moment), I'll warn the pilot that he might get a little nudge!).
And finally! It isn't a legal requirement to use the 'Heavy' suffix in the UK but I never object to it. The Yanks love it and the DLH too! Doesn't to any harm. I'd rather every heavy reported being heavy than a single oik who doesn't report their passing altitude and their INITIAL cleared altitude. That really annoys everyone!