YouTube video SEO

When optimizing my 200 YouTube videos;

I'm promoting a generic tshirt website using YT videos, so should I simply use as many releavant "tshirt" keywords as possible for each video?

Are there adverse results if I use this same large keyword list for all my videos?

In the description, I know I need to place my URL first but is it better to have a description about my tshirt site or about the video itself for each video?

Usually I try to add as much keywords as possible but I have also got good results with little but relevant keywords.
About the URL, it should be placed first as it can increase CTR.

Sent from my Galaxy S2 using Tapatalk.