After they have cooled enough to touch them, I start attached the suckers. It's according to personal preference, how you want to attach them.
I have tried in the past to coordinate them by size, but I like the look when they are all mostly the same size.
It is also according to personal preference whether you like 1 row or 2 rows of suckers. To me, a tentacle looks weird with only one row.
NOTE: You will have to press down and pinch the tentacle slightly to get them to attach, be careful not to flatten the tentacle. You may want to use tweezers for this step. I didn't have any and I think fingers are fine.