I don't know for 100% certain that you need to uninstall Office 365 prior to installing Office LTSC, but you probably need to. I would uninstall/reinstall to be sure it is installed properly. There is no reason not to.
I think Office 2024 only comes with Outlook "Classic". So, no worries there.
None of your Office files should be lost. Make sure you have a good backup just in case it goes sideways. Well, maybe if they are stored in OneDrive.
They only real downside is that O365 includes 1TB of OneDrive space. That will go back down to whatever is "free" (15GB ?). I don't what happens to your data when the subscription expires.
They used to offer affordable OneDrive-only plans ($20/yr for 1TB), but they stopped. No worries though. You can buy a 4TB USB3 drive for ~ $120, and this puts you back in control of your data.