[TRP]

Hi Twister. I don't think platform tickets are used any more, but if you have a travel ticket it would be fine & some of the smaller stations are open to access anyway (such as Robertsbridge - see photo below).
With regards to Ashford, I haven't visited the station (except when changing trains), I generally go to a footbridge just to the North West of the station which links Victoria Road (next to Victoria Road Primary School) to Elwick Road (just about opposite County Square shopping centre). It's a good vantage point which allows views of the lines to Tonbridge and Maidstone as well as a (restricted) view of the Eurostar lines. There's some photos below showing some of the variety at Ashford, but no freight on that occasion.
However, I have had a thought that Tonbridge might be just as good (if not better) for you coming up from Hailsham. I haven't been there for some time (except passing through on the train), but I think it should be a good spot. I think some of the Channel Tunnel freight trains go via Tonbridge (although a lot go via Maidstone) & you would also get the gypsum trains to/from Mountfield. Also, Tonbridge West Yard is heavily used by GBRf for freight trains and a base for some of their locos. This is straddled by a footbridge which appears to be publicly accessible from Clare Avenue or Douglas Road.

Regards,

Tony