Hille and Gumbleton are certainties to return from long-term injuries, while Williams will play his first official game in the red and black.
Howlett, who was elevated under the nominated rookie rule last week, will also make his debut as a Bomber.
"It's been a great pre-season from the perspective we've had most guys fit and raring to go," coach Matthew Knights said on Tuesday.
"We've got a good dilemma at selection. We've got a lot of first-, second-, third- and fourth year players battling for spots.
"Hille and Gumby have been picked in the 22 and it will be great to have them out there. Essendon teams have run out so much over the past 12 to 24 months without them so it is going to be great to have them back"
Pre-season draft acquisition Kyle Hardingham will also be named in the 25-man squad.
Suspended trio Mark McVeigh, Nathan Lovett-Murray and Michael Hurly are expected to play in a VFL practice match.
Knights said the season opener against the reigning premiers posed a great challenge for his side but it was one he was confident it was up to.
"I believe the Cats are in good shape; they won last year's grand final but they also won their last practice match by seven goals in Western Australia.
"They have outmuscled us and really had their way with us over the past two years [but] it's a new season.
We're really positive about what we've done in the pre-season and the players are in a good frame of mind."
