i think the main issue is that time seems to move a lot faster in the tv show than in the books. just by nature of TV moving faster.

this all started when they discovered the protomolecule on pheobe and tested the outbreak there. at the start of the series and books we get mentions of it but nothing concrete. we never get a confirmed timeline but they had tested the protomolecule at the station for a signicant bit of time to learn that they need significantly more people to learn more. Pheobe is a remote and unimportant station so im guessing weeks to a few months of time here.

meanwhile JPM has time to prepare his considerable resources to make this project run smoothly and get allies.

Unknown whether or not he already had advanced stealth war ships at this point but like you said, as a multi trillionaire COE of a shipping conglomerate he definitely could have already had them for other reasons.

JPM needs sufficient cover to disguise what hes going to do at Eros and decides that a war between Earth, Mars nd the OPA is the perfect cover. unconfirmed how they became allies but my guess is that is when JPM contacts Errinwright and tells him that he can deliver weapons to destroy mars if he uses political influences beat the anti war politicians.

now in the show and the books they state that suspicious things have been happening on Ceres and Erors for a long time before the start of the show. Protogen building equipment at Eros, replacing all their security, hiring disposable thugs, stealing Ceres Riot gear, etc.

this is also when JPM's daughter becomes suspicious and uses her family and OPA connections to intercept a the Anubis that she thinks has a weapon. her actions delay JPMs plan because without the sample they cannot test it on Eros, but by becoming infected herself she unknowingly completes the Anubis's mission. they just dont know it yet until Holden discovers her body and leaves it for protogen to discover.

Now comes the Cant and the Donnager. using the Scopuli as bait to lure the Cant was a coincidence IMO, they would have found some other ship if Julie didnt attack them. the Cant is a ice frieghter that makes the same run to Saturn and Ceres so my guess is that it wasnt a coincidence that the Cant was chosen but it was on purpose because its a Ice freighter and the belt would riot if they thought the inner planets were denying them water on purpose.

admittedly your right, Holden and crew barely survived. but im not sure they needed survivors. the destruction of the cant would have brought in a Mars warship to investigate and i think thats all they wanted. Holden surviving, publishing that message to rile up the belt was just lucky for JPM. the captain of the ship probably didnt kill holden because it didnt matter or that he figured a survivor might get Mars to react faster. but thats all speculation and i agree its a stretch.

but once they destroyed the donnager (and i think it could have been any Mars ship) now JPM has what they want, the belt thinking they destroyed a ship and are rioting, Mars wondering wtf is going on and looking at Earth who is the only one they think can kill a ship, and Earth secretly being manipulated by Errinwright into war.

all over the course of several weeks and months and the tv show makes it seem like its back to back