Birmingham is not to be confused with farms. Machines can not be sold. Once machines are hired they work for you indefinitely, providing you with an unlimited amount of BHAM at a starting rate of 10% hourly.
Strategies are personal, you either strictly compound, strictly withdraw or you do a healthy combination of both. In our opinion the best strategy is to compound as often as profitable, considering transaction gas. Once you're happy with your daily, weekly or monthly results, take profits as often as you see fit and simply continue compounding the rest.
Keep in mind that the 10% hourly rate is not completely constant, it will vary slightly based on a combination of factors, including your personal hiring, withdrawing, compounding habits and the habits of the community as a whole. Your personal habits hold much more weight in regards to your overall personal returns. Just as your hourly rate can decrease it also increases based on a combination of those same habits.
After hiring any number of machines, you will begin to see returns very close to the advertised 10% hourly, this number will rise and/or fall based on the factors explained above.