You can use up to 120 characters for each of your keyword video tags at Youtube. Typically I like to use about 15 to 20 tags.The following statement comes from Youtube in the self help area.
Here's what YouTube says about video keyword tags "Enter as many tags as you'd like into the tags field" Just keep in mind it is not a good practice to use video tags that are not used in your newpaper articles converted to video.
Lets say you have some articles about online business marketing listed in business newspapers that you want to create article videos for. Some good keyword video tags you could use might be, "online business marketing","How to marketing a online business","online marketing", ...
