1. Cachly does have this feature. If you turn on Proximity alert, you can leave Cachly and it will alert you for caches nearby. In the Live tab, it will not continue to load caches and that could exhaust your API limits during the day. Instead, I would save caches to an offline list, then turn on proximity alert for lists.
2. Adding friends IS possible in Cachly. Go to More > Friends and you will see your list of friends in Cachly. Also, going to a users profile and tapping the + on the top right will allow you to send a friend request. Third-part apps have limitations, please see: https://help.cachly.com/article/52-friends
3. Hiding your own caches it not possible on third-party apps. What do you mean by uploading your trackables?
4. This might come in a future version.