Salting meat before simmering
There has been quite a bit of back and forth among chefs on whether to salt meat well-before cooking (up to 24 hours) or immediately before cooking.  You might find this interesting. The article points out, according to Harold McGee, that a large amount of salt (typically the amounts used for curing) does indeed draw out moisture, however, the small amount of salt used for seasoning allows the cell structure to retain water.  The author goes on to test several proteins, none of which are stew meat.  My interpretation of this work, for your situation, would be to salt ahead of time.  Further, I might try two batches of stew, one where I salted the meat 24 hours in advance, and another where I salted immediately before browning.  Why not add the salt later?  Well, I think you have a greater chance of drying out your stew meat if you don't salt first. 

In addition to salting the meat, you will want to adjust the seasoning of your stew at the end, as water will evaporate and the flavors will concentrate.  Seasoning is generally not a one step process.

Pepper is another story.  Some people have an aversion to the flavor of cooked pepper, which can take on a bitter note.  In this case it can be added at the end of the cooking process.