Considering the direction I am coming in from, I would select a waypoint (and include it in my flight plan) for the destination that would be the first waypoint in a STAR having a final approach to a particular runway/s.
In fact if you are on a published Route, these will normally have a Waypoint that transitions in to a STAR. If you are on a non-published Route you might get an Amended Roue Clearance or simply get vectored for an IAL if required.
My first question is - if there was a change of runway or inbound direction rendering my planned STAR unworkable, where and who can I get the new STAR from? Is it with Approach or something further like with Radar ?
Most STARS will use the same point for either Runway, or may in fact be applicable to 2 or More Runways, so the STAR does not need to be re-issued, just the Runway. If your FMC can handle it punch in the new Runway. If it can't, or if your profile is now no good, just task for vectors for xx track miles.
My second one is - If I did not nominate a waypoint for a STAR, will I be given one or will I be radar vectored instead for an instrument approach ?
See First Answer
And lastly - in regards to heavies, I can only assume that they have pre-programmed their STARs into their FMC even before departure, would ATC change this for any reason ?
Not sure anyone would get too far ahead of the aircraft in this regard, but will obviously aniticipate it a couple of hundred miles out - to no doubt get changed anyway!
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As far as STARS being an ATC thing, this is essentially true. STARS are designed to segregate ARR and DEP through LAT and VNAV requirements - also significantly reduce the amount of RT, which is a blessing when busy (for you and for ATC). Also give you accurate Track Miles for your descent planning. Although not neccessarily in YSSY where the STARS have a lot of Route Discontinuity and you get vectored to final anyway.