I've been installing softeners and other filtration equipment for over 15yrs. We always install softeners just as water enters home. Sometimes we will plumb all outside faucets before filter to conserve except for one that can be used to wash car. I would recommend you have your water tested. You need to know pH, iron, and hardness levels, and TDS would nice too. You will need to know hardness level to setup softener, if iron content is higher than 1ppm or mg/l I would suggest you install a iron filter before softener, but before you can install an iron filter the pH needs to be higher than 6.8 or it will need to be raised with pH adder or if its real low you nay need an acid neutralizer.
The reason to take care of iron if its a high level is that it will iron foul your softener and ruin the media in as little as a year if iron content is high enough. We have a filter that works real well and there is probably a dealer in your area since its a worldwide company that makes it, that will work on all three problems but the water has meet certain criteria.
Hopes the helps. And remember you can always add more filtration in front of softener as needed.