My pond was designed by the NRCS and has several of the features you are referencing and I couldn’t be happier. The 3:1 slope is highly recommended for safety. When mowing on the back side of the levee, it is almost impossible to do it safely with a slope of less then 3:1. 4:1 would be even safer, but requires a much wider base and therefore more dirt to move and more expense. With regards to the safety on the water side, if you have a steep slope like 2:1 with no shelf, it is very difficult to get footing and climb out because you keep slipping back in. Think for example of trying to climb out of a creek with a steep muddy bank versus climbing out when there is a more gentle slope. With regard to a “shelf”, there are both safety and erosion benefits. The shelf in my pond was built to be about 6” lower than normal pool. So, there is the top of the levee, then there is a 3:1 slope down to the level of the outflow pipe resulting in 2 feet of free board. Then, 6” lower than the outflow pipe there is a 6-8 foot horizontal shelf which basically has 6” of water covering it and then the slope starts again at 3:1. If someone falls in, they can swim over to the shelf and crawl out into the shallow 6” of water and then easily climb up to dry levee. The shelf also reduces erosion from wave action because the waves break apart in the shallow water before hitting the bank. When water levels go down slightly, the shelf becomes somewhat dry and weeds are easily managed. Go with no less than 3:1 slope and also a shelf, you will be happy you did.