How do I calculate the expected shares per minute for my pool
I was able to find some information from this page...

https://arxiv.org/abs/1112.4980

I think I was able to figure out the formula, but somebody please correct me if I am wrong. The formula is not very difficult, but you must know the number of hashes that correspond to a minimum difficulty of 1 (share difficulty). This is easy to find for some currencies (bitcoin, 2^32), but very difficult to find for others. For Zencash, it is 8192 or 2^13. The formula to determine the expected blocks per minute for Zencash is:


  blocks_per_time = (hashrate * seconds) / (8192 * block_difficulty)


In our case, the estimated blocks per minute would be:

(50000 * 60) / (8192 * 764414.6217) = 4.791e-4 blocks/min.

Then if we know it takes an average of 764,414.6217 difficulty-1 shares to solve a block, then we can calculate the pool's shares/min as:


  shares_per_min = blocks_per_min * block_difficulty


shares_per_min = 4.791e-4 * 764414.6217 = 366.2.

Or, we can simplify the original equation to estimate the given shares/min in a pool based on a given pool hashrate as:


  shares_per_min = (hashrate * 60 seconds) / 8192


shares_per_min = (50000 * 60) / 8192. = 366.2

Based on this (and the reason I wanted to know the answer to this question), you can see that if you stop mining on a PPLNS pool with a steady hashrate of 50 kH/s where n=20000, you're estimated reward should fall to zero after about 54 minutes. Of course, your shares are very likely submitted at a higher difficulty than one, but this shouldn't affect that calculation.