The signed area asks a lot of questions and one of them is Post link to your signed contract.
Can’t you just make it autofill a signed contract with the prefilled fields and then allow the user to add things such as pictures / descriptions without going manually and creating a new post?
Of course it would have to only work for those who link their usernames.
Just a thought as I did a signed and it was a lot of info to put in.
Or Better yet, start with the calc and have it fill in Signed but calcs are much more difficult to get right as I found out with my ‘hidden MSRP’ deal.