I’m pretty sure the answer is yes. As long as you sign the extension before the contract concludes on June 31st you can give the 8 years.
Nope. The criteria is "latest trade deadline".
So actually, Erik Karlsson could not sign an 8-year deal with San Jose until after this year's trade deadline, because prior to that, he was on Ottawa's list at the previous trade deadline.
Here is what I found in the CBA:
50.8 Prohibited SPC Terms and Practices.
(a) After the execution of this Agreement, no SPC may provide for:
…….
(iv) An SPC with a term of greater than seven (7) years, provided, however,
that a Club may sign a Player to an SPC with a term of up to eight (8)
years if that Player was on such Club's Reserve List as of and since the
most recent Trade Deadline. With respect to potential Unrestricted Free
Agents only, the ability to re-sign a Player to an SPC of eight (8) years
expires when the Player becomes an Unrestricted Free Agent. With
respect to a Player who becomes a Group 2 Restricted Free Agent, a Club
may sign such Player to an SPC with a term of up to eight (8) years
provided such Player was on such Club's Reserve List and/or Restricted
Free Agent List as of and since the most recent Trade Deadline.