One post can be as big as ~32 000 characters unless administrator sets it differently. Because I have seen/made posts longer than 15 000 characters at this forum we can safely assume that two posts one by one - will give you at least 30 000 characters of space. Which should suffice any needs. In case it doesn't - you've made a terrible designing error with releaving it that soon.
Conclusion: It is safe to reply.
Reason for writting it: What you want to do seems to be a pretty big project. Why not to allow users to reply and apply as helpers for the project?