How long is a piece of string
For something simple follow the example of TV and film programmes and fill around 2/3rds of the screen width.
Insanity is hereditary, you get it from your children.
With regard to font type, Premiere Elements seems to default to "Adobe Garamond Pro" for the Default Roll. Arial seems to be a close to it, but I see a subtle difference between the two that pushes me in the direction of Adobe Garamond Pro if I had to choose between the two.
It is important to explore and experiment as to the best font type and font size for your particular situation, especially as it relates to the background for the rolling credits and how fast they are rolling. The contrast between the font color and the background color for the font can strongly impact the clarity of the rolling credits.
I would not give one person more than two lines, one for the name and one for his/her title.
Thanks as always for your help. I will experiment and see how it works out. If I discover anything interesting, I will share it with the group.