You are in the midst of the learning curve.
The only time I have had any problem wearing Stealth to sleep was from the constriction of early morning erections caused during testing of new designs or combinations of sleeves, Retainer bands, Sabre Skins, etc. that were too tight.
Urination is possible when standing up. The fit should be dialed in properly otherwise if the urethra is stretched or compressed too thin. This will result in a burning sensation which causes the body to stop the flow of urine.
I have experienced the sideways stream on occasion as well, but this has not been a regular problem for me.
If I am wearing the spandex sleeves or Sabre Skin, I generally remove them to ensure complete elimination of urine. If you rush the completion, you will be likely to experience leakage or even a spurt of urine with a sneeze later on. When this happens, it is very uncomfortable and potentially embarrassing. The trick is to take time to relax and eliminate with 2-3 extra contractions of the PC muscle than usual.
Make sure you take a break for a few hours or overnight if you experience any pain or irritation wearing Stealth. The sooner you rest, the sooner you can resume wearing again.