Maximum per pen is 20, but personally i go for 10 pig per pen.
Slaughter the largest animal, as time goes the smaller one will grow pa unless it is bansot. Theoretically hindi ka malulugi.
The trend in swine is this:
swine raiser - middleman - meatshop -consumer. Example, the middleman will buy the hogs for 85-100 pesos per kilo then the middleman will slaughter it and will sell it for 120-140 kgs then the meatshop will sell it for 160-170, to this extent, figures are not exact.

. So all in an pera towards you.
Remember that once the animal is slaughtered it will lose about 10-20 kgs (intestine etc...) IN the meatshop different parts have different price and some parts are not that salable( head, pata)