Personally I've been including at least five Trainer cards in each deck I've been running as I like having access to the extra bonuses they offer, but you're free to add as many or as little as you like
If so please let me know in the comments.
The creature won't get an additional +1/+0 if you draw another card later in the turn
As the event happened back in 2016 and only for a limited time, there are quite a limited number of these cards in circulation, increasing their value significantly
Check out our article on How Grading Works for Pokemon Cards for a break down of the grading criteria and the grading scales for the 3 major Pokemon grading companies (PSA, CGC, and BGS)
Pull rate from Regular Packs: 2.38% The estimated pull rate for Teddiursa (Wisdom of Sea and Sky) from a Regular Pack is approximately 2.38%, meaning you might need to open around 43 Regular Packs to obtain it