Communicating, organising and managing team expectations as early on as possible is really important.
Get your dates out there, even estimated dates, as soon as you can. Doing this will enable team members to start make arrangements to be away from their lives, and make it more likely that as many of your team members can make it as possible.
I'd recommend creating a separate channel to communicate retreat details. Make it somewhere they can ask questions, catch anything you’ve missed, ask questions, and go back to when they need to. It can also become a place to create buzz and excitement around your trip!
In that channel you can also keep an eye out, and get a vibe on what people's concerns and expectations are - so you can take them into account when planning. It can also become a source of information and stops you from being asked the same question multiple times. Keeping an eye on the chat can also give you some really nice ideas on what people would like to get up to whilst they're away, and mostly importantly - often what they’d like to eat.
Transport
Getting a good understanding who needs to get where early on will save you lots of logistical planning. Booking transport in a rush is not fun. It can also work out more expensive. For many people travelling long distance can be a big deal - anxiety inducing even. Having the time to be well organised can give them peace of mind if they’re the type of person who needs it.
If your company allows for it - let people book their own flights. Not making this part of your job will save you multiple nightmares - particularly when it comes to the day of travel. It’s likely you’ll be unavailable at the time of their travel, as you’ll likely be traveling to, or on location making last minute arrangements. The last thing you need is to be sending people their boarding passes and flight times. People are far more likely to take ownership of their travel if they have planned it themselves.
Centralise your teams travel plans. Having a place where everyone can get the information they need about anyone in the team will save you a lot of time answering questions.
Visas
Applying for visas can take time, make sure that individual team members manage their own applications, of course with your support. Often countries don’t allow for applications to be submitted prior to 3 months before travel - but having as much time as possible will be a bonus.
Creating a separate channel for those who are going to need advice and supporting documentation is a really good idea. Helpful discussions can take place in relation to what the visiting company requires, and again saves you from being asked the same question in multiple DMs.
Agenda
Start working on your agenda early, even if it only provides estimated dates and location and link to it in your retreat channel. Update the document as your planning unfolds and becomes more certain. Update the channel at the same time and it will act as a reminder that the retreat is around the corner. It'll also nudge team to ensure they’re doing the bits that are required of them to get there.