Can I feed/water every 2/3 days ?

No, not really boss. You really have to keep that growing substrate moist when using coco. It probably wasn't the best choice for someone who has a busy schedule but we're here now so let's see what we can do. I really recommend getting an autodrip system hands down. It's your best option and it's really cheap if you know where to look (Amazon obviously). They do have globes that you can fill and stake into your pits that will feed/water your plants or you can use wine bottles but they really aren't the best choice for coco and nutrients. I'd go with the auto watering system from Amazon that you can put on a timer and fill a reservoir with your nutrients/water solution that will feed that said system. Hope this helps.