Certainly white tape is very useful around a training paddock, but once they are trained the use becomes unnecessary and an extra cost. Surely the electric fence posts are a good enough indicator to a pig to exactly where the fence is?
Yes the white tape does sag, but can be easily tighten(especially if you have isolators on each paddock).
Certainly would never use barbed wire to put around a pig pen(I know both Blonde and Happy Hippy use it) as it is totally unnecessary and I would have thought harmful to any animal that tries to run through it.
I suppose it just hinges on what you prefer.
As to the battery or mains I've used both and yes the mains is stronger, but batteries(heavy duty liesure batteries) work equal aswell and don't become a problem if you carry spares and you continually charge them systematically.
It will also depend on how conveniently place your mains supply is and the extra cost it may incur?