There’s still a lot of time for injuries or underperformance to happen, but right now you don’t really need to worry about having money for any other additions. The rotation is spoken for, with Smyly, Montgomery, and Azolay being depth options. Wilson is the only reliever leaving, and Smyly needs a roster spot plus Maples and maybe another downstream arm are optionable pen possibilities. If you absolutely need to free up money, selling off Zobrist is the easiest option, assuming that Happ is a functioning major leaguer and they don’t mind him getting some infield time(La Stella and/or Bote being IF reserves is also a possibility). You don’t have to get rid of Heyward and you definitely don’t need to attach a player as valuable as Happ to him to make room for Harper.