Sex is sex of course it's fun!
Some popular baby shower games are bingo, pregnant twister, guess the sex, and other games. Many of these require no extra money and can be done with supplies you have around your house. http://www.parents.com/baby/shower/games/fun-baby-shower-games/
you have a shower
yes!
Because Sex is fun. If not you would not do it.
sex
Babyshower101.com has a great list of baby shower games to play. You can also find a list of fun games at parents.com/baby/shower/games/fun-baby-shower-games.
SING!! masturbate
both
Yes you should
you bring someone else inside with you!
Yes, and if your do that you might as well have sex, oral sex, 69ing, and other sex things
There is missionary sex, dogging sex, woman on to sex, shower sex... just look up sexual positions on wikipedia.com