I was on W2 from Jan to Feb 2017. Beginning March 1, I became an independent contractor. If for example, my expected income from March to August is $100k, and I don't really know if I'll still be a contractor starting September (I might go back to being on W2):

1. Should I base my estimated taxes on $100k and divide it by 4?
2. Since I've only been a contractor for a month, is it okay to start paying estimated taxes in July?
3. Is it possible to change my tax payment in October if, for example, my contract is extended and my taxable self employment income increases?
4. If I go back on W2 starting September, should I keep on paying my estimated taxes until January?

Thanks,
J