When you attach the arms to the torso and if theirs a gap, is the best way to fill this in is to just use putty?

Pat,
I think it really depends on the size of the gap.
If it's pretty thin just try plastic cement or superglue.
For a slightly bigger gap mix some baking soda with the glue (and then file/sand the excess virtually straight away)
You could even try stretching some sprue and laying that in the gap beforehand.
good Modelling
Tom

best bit about 1/35 figures is the uniforms. all the folds and highlights. cant do faces tho. good luck

You can thin a bit of Tamiya filler putty with acetone free nail varnish remover (note it must be acetone free else it'll chow your plastic) and apply it to the gaps with a brush or even toothpick.