Definately agree that less is more, two wires are more than enough to cause confusion,
 
 Speaker flex is about the best, but not the gold plated stuff, keep that for ZZ Top,or Kylie,
 
 Also start the way you want to continue, I like track power by battery, with loco battery back up, with radio control, its simple for me, but I looked around for a long while, made a shortlist of wants, and not wants, layout is 90 yards long so far, total cable for power supply is 2 yards, 
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 Experience  has  taught  me over many years of G scaling,  in  the  interest  of  sanity  to  keep it  very  simple, 
   
 When  I  lifted  an  old  (analogue) line  some  years  back  prior to  moving  I  filled  several  Black  rubbish bags  with    cable 
   
 Whilst  doing  this  it  was very apparent  that  over   the  several  years  of  the lines  existence  probably 75% of  those  cables  had   served  no  real  useful  purpose 
   
 These  days with  digital  system in  use  I  have  but  2   feeds  to  the  line  one  close  to  the central  station  the  other  at  some  distance from  the  C.S. fed  by  a  simple  'speaker Cable' ( 20-25p per metre  local Hardware  shop. 
   
 When laying  the  track  I add a short 6" length of  the  same  speaker  cable  ,  at infrequent  intervals around the  line, simply by insertin  the  bared  ends of  the  cables in  the  rail joiners of LGB track, or utilising  the  screws UNDER Aristo track,  these  cables  are intended for use in the  event of  an unexpected power failuer in the  track, it  would be  a simple  matter  to  connect  a cable  to a GOOD section of  track and  thus  restore power,  in practice  this  has  very  seldom become  nescessary, the  best  conductor of  the  power  is  the  track itself! 
   
 As  I  mentioned  earlier  keeping  it  simple  will pay dividends