I'm only answering the second part.
The ejaculate is made up of less than 5% sperm, the rest is made up of seminal fluid and prostrate fluid.
Seminal fluid is produced in the seminal vascules and is made up of sugars hence the sweetness.
Prostrate fluid is produced by the prostrate gland and is high io mineral salts.
The flavour change to bitterness is caused by bitter urine along the urethra and not the ejaculate itself.
Sweet or salty depends on the ratio of seminal to prostrate in the fluid.
