Hi, I’m planning to hike the long trail with a small group of friends starting early mid June. Do shelters and campsites usually fill up quickly? Is there space to put up multiple tents around the shelters? Should I be planning a backup shelter each night? I’m beginning to plan right now which shelters to stop at and where to restock so any tips are appreciated! Thank you!
Definitely bring a tent, even if just as a backup. Don't expect space in a shelter every night... It's a popular trail, and shelter space is first-come, first-serve.
Having a tent also gives you a lot more flexibility in your itinerary- you don't have to stop at a shelter each night. Keep in mind too that if you're playing to hike the full trail, you're almost certainly not going to be able to adhere to a set itinerary you put together in advance. It's good to research the trail to be sure (and I'd strongly suggest carrying a physical map and not just relying on hiking apps alone). But over 200+ miles, flexibility in your itinerary is going to be key.
Some of the shelters have designated tenting areas that you're supposed to use if the shelter is full or you prefer to tent. It's not always the space immediately surrounding the shelter but it's usually close by. In a couple of cases, though, the designated tenting area might be a short hike away (half mile or so).
How many people are in your group?
Download the FarOut app and buy the LT map on it if you have not. Rather than planning a specific shelter in advance, just plan for how many days between resupplies and plan where you want to do that. Flexibility is useful (ESPECIALLY in a group). In general, shelters have plenty of tenting options as well (except a few up high)
You will almost always be able to find a spot for a tent. Some shelters dont have great tenting options but I've never not been able to find some kind of usable spot. Maybe not a spot in the shelter but staying in the tent is nicer anyway. Don't worry about it too much.
No point in planning on where to go every night before you’re out there. Planning on thru hikes is largely useless. Just get out there and go for it.
1st 100 miles nobo you share with the AT. At that time, there should be a smallish-medium sized bubble passing through. I would consider a hammock over a tent if you can because tent sites aren't great. the first 100 miles you will be fighting for shelter space w. ATers, and many will be dicks to you bc they think they have more "thru hiker cred." I saw it while on the AT myself and was telling them to leave LTers alone and let them HYOH. Just prepare for some minor "turf wars" at shelters related to that during your first 100m nobo.
You are right to plan for some full shelters and priority is given to thru hikers by the caretakers (where they exist) per the Green Mtn. Club
You shouldn't have much trouble finding a place to pitch a tent