Welcome to the forum Mo.
1. A great investor once said that the richest people in real estate buy properties and hold them not flip. That's how you really become wealthy in real estate. That being said initially it can be good to start flipping and rent out properties as well. A mix of the two. For me the only reason I flip is to get capital to buy more buy and hold properties.
2. There is not set time, it really depends on many many factors such as your market, condition of property, contractors, permit approval time etc.. However, there is almost always a learning curve so the more properties you flip the easier and faster it will be to flip the next one.
3. Purchase price, sale price (ARV), market (demographics, job growth, housing supply/demand etc..) any deal can work as long as you can buy a property for less than you can sell it for but it may take some research.
4. Look at the numbers and trust the numbers don't think that because you will renovate the property better than everyone else you will get a higher price. Assume the best prepare for the worst. Always be conservative in your numbers.
5. Know your market and work out the numbers.
6. I love doing real estate the whole process of flipping a house giving someone a great product and seeing that your work helped someone else. It's interesting and gives me financial independent.
I live in NYC myself and I strongly suggest people from here to start investing out of state but somewhere close by so you don't have to rel completely on other people and if anything goes wrong can drive to the property and take matters into your own hands. People I talk to from the city get shocked when I tell them how many properties they can get out of state for the price of one property here. You can 3 - 4 times more cash flow in other areas. That's why I started out in NJ and it has been working great for me. If you need help you can message me. Best