Personally it’s been a long time since I didn’t have a quick link but I would not break the chain where it was last joined. And I would use a reusable quick link if possible (kmc do them). I use the Shimano quick links that come with the chains for the saddlebag for use in an emergency.
For the spacer you’ll want the 1.85 spacer when using an 11 speed MTB cassette on a road freehub.