You will need fluent Spanish in those areas... as very very few people will be able to communicate in English. Your knowledge of Spanish will be very handy !! ^
Without wanting to alarm you and not knowing exactly where you will be staying, all the areas you mention have a high degree of "variability". What I mean is that while there certainly are some nicer residential areas in Villa Martelli, some parts will warrant caution. General San Martin and 3 de Febrero are areas I know much less... and while they too will have 'better' areas, you will still need to watch out about surrounding areas.
By 'variability' what I mean is that you may have a couple of blocks that are perfectly fine.. but in some areas one block can mean the difference between middle class suburbia and an an area where the Police dont go unless they have SWAT backup.
Knowing exactly where you are going, not taking a wrong turn and getting into more difficult areas will be key. Also, I dont know if you 'stand out' as a Foreigner... but this may also be an issue. I assume you have locals that live in these areas and they will of course be best suited to give you exact & specific advice on these areas. How will you get around... will you have your own car..???
All in all, please take all the above with a pinch of salt as Im by no means an expert in any of the areas you list above...
Cheers,
Gaucho100K