I also use different own domains with catch all email addresses. The only thing I have doubts about is how much accounts I can make without taking any risks. For example 3 Instagram accounts on 1 IP with the same unknown domain name are easy to discover.
I really do not know what kind of algorithms they use. Maybe I am worrying for nothing.
I am anyway wondering sometimes... If they really want they can discover fakes so easily... My private account I use with a home IP, sometimes on my macbook. Sometimes I use it on my phone. It has different IP's depending on location. Sometimes I follow 10 people. Sometimes days nobody. What will they think about 1 account following 1000 people a day with a fixed datacentre IP ?