No one answer- sorry.
Yes, any 98 stock will fit.
The best trap gun you can buy is one that FITS you and breaks the clay. Get one that has a adjustable stock. You need to pattern it so it hits where you look. A TRAP gun will shoot higher than a field gun. Lots of useful information on the Internet, do your homework and pick up a nice used one.
A Tippmann carver one with e trigger.
It will only fit the X7 and the A5. You can buy a model 98 version which will work with the 98 series, alpha black, project salvo and carver one.
You have to make one
No one knows what the purpose for the stock pen, theories are that the stock pen was used for extra guns,gun powder etc.
They are the same gun, except for the carry handle, body look and number of rails. Neither is better, unless you want the carry handle (alpha black) or rails (carver one) There are literally no advantages to either over the other.
The new Azodin ATS and Tippmann Carver one are two you should look into for beginner markers.
The best gun for any application is the one that you fits your hand properly and that you can shoot accurately.
Why would you want a plastic stock. I have this gun with a plastic stock and am considering replacing it with a wooden one. If I do, I will certainly be willing to sell the plastic one.
There is no one gun that is gender exclusive. For any person, male or female, the best gun to carry is a gun that fits the person's hands properly, and that fits the person's carry requirements. Some people want a tiny pocket gun, some women want a gun that can be dropped into a purse, some women will actually carry a gun in a holster, so, in short, it depends on the person.