Because everyone is so different in terms of symptoms, there is really no answer to your question. There are people who can live just fine with counts around 20,000 and then there are people who have bleeding even when they have higher counts. I know it can feel scary in the beginning, but over time you will learn to look at your symptoms and know when you might require more treatment based on what your bruising or "spots" look like.
It looks like you have only been diagnosed with ITP for a few months, so I'm sure everything is still feeling overwhelming. Do you have a hematologist? In looking at your description, it sounds like they have only tried steroids and IVIG on you so far? There are so many treatments for ITP that are available today that can help you manage ITP without requiring you to be hospitalized for IVIG infusions or dealing with the horrible side effects of steroids. Some of the drugs that people are using for ITP nowadays are Promacta, NPlate, Tavalisse, Doptelet, Rituxan, and many more! If your doctor is just trying to manage your platelet counts by giving you IVIG or steroids and is not suggesting other treatments, you might want to talk with them about why they aren't trying other treatments. If your doctor does not have a lot of experience with treating ITP with modern treatments, you might want to shop around for a new hematologist.
Many of these treatments can control counts very well for most people and will keep you out of the doctor's office and out of the hospital! Reading about ITP is also very helpful in the beginning, so you've taken a big step in trying to learn more about the condition here, which is great. Feel free to ask any questions that you may have and don't be afraid to ask your doctor questions if you don't feel like your treatments are working for you. There are many doctors who don't know a lot about ITP, so keep that in mind. Best of luck!