Personally Id recommend the via Rye route:
assuming you're coming from London you get:
High Speed Main Line (from St Pancras)
or Ashford main Line (from Charing X, Waterloo east London Bridge)
or Hastings line (from Charing X etc.)
then Marshlink Line (oddball rural diesel line with single line running)
New Romney is the limit of the Rye plusbus area and has a 2 x bus per hour service from outside Rye station.
The bus journey in itself is interesting going past Camber sands along the English channel, across Romney marsh and over the Dungeness branch at Lydd.
RHDR is about 10 mins walk from New Romney High Street. New Romney station has the advantage of being the HQ of the RHDR cafe, model railway, engine sheds and being half way down the line you can do which ever half suits your schedule first.
Rye is a interesting hill town in its own right and has a lot of good pubs eateries etc ifr you want a break on the way home.