I got to 8b second try. Get to the most valuable property as soon as possible and then ignore everything else not worth you time/clicks. Then buy as much as you can early in the Boom when prices are lowest. When a Recession starts, start selling everything while the prices are still high. Rinse and repeat. I kept all the debts until the end.

This only really works because the boom/bust cycle is too predictable and consistent, so it really just becomes a 'how fast can you click' game. It would be better if a) more random boom/bust points, duration, and rate of rise/decline, and b) buy and sell in bulk.