Maximum number of 90 degree bends in drain?
1 (one). A 90-degree "Elbow" is only permitted at an inlet's vertical (i.e. what a sink's p-trap assembly or toilet's closet flange drains into). After that, you should only use a Long Bend 90 or 2 - 45's. In other words, there shouldn't be any "Elbows" within the plumbing system, since they slow the water down and make Drain Augers difficult or even impossible to use.
I couldn't find what I was looking for to give you an official reference, but the maximum bend allowed is 135-degrees. For example, a 90 and a 45 or 3 - 45's. If you need more, you're doing something very wrong and need to reconfigure your plan. Also, always use Wye's whenever possible for any orientation. Tees and Sanitary Tees should only even be used vertically.