I do think Ricketts will be willing to go over the luxury tax threshold, so that's where I think they'll get the space. That said, I could definitely see them packaging Heyward with a Schwarber/Happ in a deal where the Cubs maybe pay half his due money. Heyward can still play and someone will want him if the Cubs can make the money thing work.
Here's where the Cubs stand right now for 2019 (all numbers are base salary per spotrac.com). The Cubs have $144M currently locked in for guys already signed for 2019 plus Heyward's player option. There's another $46.75M in team options. $20M of that is Hamels, so there's some space if the Cubs opt to not take his option and the $10M for Kintzler likely won't be picked up (EDIT: Since posting, I've learned there's also a $5M player option for Kintzler, which I'm assuming he'll take). I assume they will pick up Q and Strop, so that's $16.75M. They're also likely going to see $36-40M in Arb deals and the rest of the roster will be under $800k.
Places to cut: $20M for Hamels if the Cubs don't pick it up (Rangers would even be paying the buyout). $10M for Kintzler, $3M if they move or drop Russell. I think Duensing will be moved, so that's another $3.5M. I don't think LaStella will be back and if Schwarber gets dealt, the pair would free about $4M. If ownership will go into luxury tax territory, then they likely have room for 1 big deal or a couple mid-tier deals.
Under Contract $124M
Lester, $22.5M
Darvish, $20M
Chatwood, $12.5M
Zobrist, $12M
Rizzo, $11M
Morrow, $9M
Smyly, $7M
Cishek, $6.5M
Duensing, $3.5M
Player Option $20M
Heyward, $20M (no way he opts out)
Team Option
Hamels, $20M (I'd guess 60/40 the Cubs pick it up)
Quintana, $10.5M (Cubs should and will pick it up. Hasn't been as good as hoped, but getting an equivalent pitcher would cost more than this)
Kintzler, $10M (Likely gone) EDIT: Again, he apparently has a $5M player option, so likely not gone.
Strop, $6.25M (He's a bargain. Cubs will/should pick this up)
Arb1
Baez - Bryant got a record $10.85M in Arb 1 year. I'll guess Baez around $6-7M, well up from the $675k he made this year.
Montgomery - Certainly added value due to starting. I'll guess he goes from $611K to $4-5M.
Schwarber - Likely goes to $3-4M up from $604K
Arb2
Bryant - Will get a small bump. Maybe he goes to $13M
Hendricks - Goes up from $4.1M to probably $7-8M
LaStella - Likely wouldn't get much bump, making $950k now. Maybe $1.5M
Russell - Made $3.2M this year. Cubs likely deal him for scraps, but between his lousy offensive year and the suspension, he won't be in line for much more than he's getting now.
Webster - If he stays in the system, he'll still be around league minimum, no more than $600K
Pre-Arb All of these guys would make somewhere between the league minimum and maybe $650K.
Almora
Caratini
Contreras
T. Davis
Edwards
Gore
Happ
Maples
Mills
Rosario
Zagunis