Do I need to get electrolites to put in their water after I get them home
Some people use electrolytes or something else, I don't. I hatch my own or get them shipped from a hatchery through the post office. All I ever supply is clean water.
A trick I've used a couple of times. If a chick is acting lethargic and not drinking or eating I take a medicine dropper and put a drop of sugar-water on the tip of its beak. You do not want to force water down its throat, you might drown it. Just a drop at a time on its beak. I actually use hummingbird liquid, you can use electrolytes or some other specialty product. The idea is that the sugar in the water gives it energy to bring it out of its funk so it will start eating and drinking on its own. plus it helps hydrate it. Through the years I've only done this a couple of times, once with a chick and once with a hen that wasn't acting right.
Since this has been so rare for me, I use what I have on hand instead of keeping something that will expire. If your mailed chicks are delayed adding something to their first water would probably be a really good idea. If you use hummingbird liquid or make your own sugar-water, dump it after 12 hours or so to keep it fresh. For the other stuff I suggest reading the label to see how they suggest you do it.
Keeping water clean is very important. With the nipple system your water should be clean, but make sure mosquitoes can't get to the reservoir to breed. The brooder needs to be dry. Some waterers, not just nipple waterers, can leak. Not all do but some do. Something to be alert for. To me a dry brooder is extremely important.
Do they need any probiotics or medicated feed or anything else like that at first?
what things should I have on hand for the chicks JIC they get sick and need something?
I'll copy something I wrote on medicated feed and Coccidiosis at the end of this. I try to give you enough information so you can make an informed decision.
On false rumor floating around this forum is that if the chicks have Coccidiosis the poop will be bloody. There are different strains of the bug that causes Coccidiosis, they each attack a specific part of their digestive system. A couple of those strains do cause bloody stools. So if you see blood in the stool you need to immediately start treating them for Cocci. But the majority of them do not cause bloody stools. They can cause loose stools, but the major sign is that the chicks act lethargic. They hunch up and fluff up, and just stand around. So if you see that behavior start treating for Cocci. Do not wait for bloody stools, they may never happen.
How do you tell the difference in shipping stress and Cocci, the symptoms are very much the same? Timing. Cocci takes a while to develop, you are not going to see any signs of it the first week or so.
Instead of filling them full of drugs or treating things that aren't there I try to strengthen their immune system from the very start. I cover that in the Cocci/medicated feed write-up below. My brooder is in the coop so the chicks are exposed to the adults immediately. On day 2 or 3 I take dirt from the run and start feeding it to them twice a week or so. This gets grit into their system from the start. It gets any probiotics the adults have into the chicks systems, that's a trick wild animals use a lot with their young. And it gets them working on any flock immunities they may need.
The way I understand it you don't have any adults so they won't get any benefits from probiotics. I'd still feed them dirt. That gets grit in their systems and your soil might have something in it that they need to start working on flock immunities. I prefer them doing that in my brooder where I can watch them more closely than running around outside. And I keep my brooder really dry, that greatly reduces the chances of them getting sick even if something is there.
Now for that write-up I mentioned.
First you need to know what the "medicated" is in the medicated feed. It should be on the label. Usually it is Amprolium, Amprol, some such product, but until you read the label, you really don't know. Most "medicated' feed from major brands for chicks that will be layers uses Amprolium, but there are a few out there mostly for broilers that use other medicines. I'll assume yours is an Amprolium product, but if it is not, then realize everything I say about it may not apply. And it is possible that the "medicated" is Amprolium AND something else.
Amprol is not an antibiotic. It does not kill anything. It inhibits the protozoa that cause coccidiosis (often called Cocci on this forum) from multiplying in the chicken's system. It does not prevent the protozoa from multiplying; it just slows that multiplication down. There are several different strains of protozoa that can cause Cocci, some more severe than others. Chickens can develop immunity to a specific strain of the protozoa, but that does not give them immunity to all protozoa that cause Cocci. Little bitty tiny baby chicks can develop that immunity easier than older chickens.
It is not a big deal for the chicken’s intestines to contain some of the protozoa that cause Cocci. The problem comes in when the number of those protozoa gets huge. The protozoa can multiply in the chicken’s intestines but also in wet manure. Different protozoa strains have different strengths, but for almost all cases, if you keep the brooder dry, you will not have a problem.
To develop immunity to a specific strain, that protozoa needs to be in the chicks intestines for two or three weeks. The normal sequence is that a chick has the protozoa. It poops and some of the cysts that develop the protozoa come out in the poop. If the poop is slightly damp, those cysts develop and will then develop in the chick's intestines when the chicks eat that poop. This cycle needs go on for a few weeks so all chicks are exposed and they are exposed long enough to develop immunity. A couple of important points here. You do need to watch them to see if they are getting sick. And the key is to keep the brooder dry yet allow some of the poop to stay damp. Not soaking wet, just barely damp. Wet poop can lead to serious problems.
What sometimes happens is that people keep chicks in a brooder and feed them medicated feed while they are in the brooder. Those chicks are never exposed to the Cocci protozoa that lives in the dirt in their run, so they never develop the immunity to it. Then, they are switched to non-medicated feed and put on the ground where they are for the first time exposed to the protozoa. They do not have immunity, they do not have the protection of the medicated feed, so they get sick. Feeding medicated feed while in the brooder was a complete waste.
I do not feed medicated feed. I keep the brooder dry to not allow the protozoa to breed uncontrollably. The third day that they are in the brooder, I take a scoop of dirt from the run and feed it to them so I can introduce the protozoa and they can develop the immunity they need to the strain they need to develop an immunity to. To provide a place for that slightly damp poop, I keep a square of plywood in the dry brooder and let the poop build up on that. I don't lose chicks to Cocci when they hit the ground.
There is absolutely nothing wrong with feeding medicated feed to chicks, whether the protozoa are present or not. It will not hurt them. They can still develop the immunity they need. But unless the protozoa are present, it also does no good.
If you get your chicks vaccinated for Cocci, do not feed medicated feed. It can negate the vaccinations.