Don't worry about the guarantor in Laos. Just put someone in Thailand or back home. I know people in Laos, but they can't expect that to apply to your average foreigner just passing through town on a visa trip.
If so, they should have seen that, unless they didn't bother to check.
With an e-visa, one must always hand a printed copy over to the check-in agent (don't wait for them to ask, do it automatically without saying anything) because without that proof, they'll assume you're coming in on visa exempt and will ask for outbound flight proof.
Forget about the guarantor part of the application form. I don't think they care what you write. Put someone back home. Or a Thai person you know (such as a spouse) or close friend or something.
NO. None of these are required at any point. Not when making an application (except using the e-visa system to prove you're in the country you're applying at) and not when entering the country.
Immigration rarely even asks for these things on visa-exempt entry, though airlines will. They won't for DTV holders though.
1 January 2025 is a public holiday. I can't see them starting applications on that date. Assume that the first working day will be Thursday the 2nd, but chances are, not much will happen until Monday the 6th, as I believe the government has designated the 2nd and even the 3rd as additional public holidays in 2025?