I am a trader by nature. I trade items and time. Not just this game but in many games. I have learned that no matter the game or the situation. You must maintain a certain level of control for things to go smoothly. For you and those participating. Everything I share with you is what I do. If you wish to use any of this. Then glad it could help you.
First no matter what you are doing (trade or visitor/shop invite) you must keep a limit to who many people can be on at any one time or even return. This is not just for your sanity but to keep players from getting impatient and running or even force leaving. Force leaving can reset player inventories. Yours, theirs and everyone elses on your island. Not always but it's a hassle. Usually no more then
3 invites at a time. With that I usually try to space the invites to. For
trades, it usually keeps them separate enough so I am trading with 1-2 while 3 is about on the way.
Turnips I try to limit to no more then 2 people at time and no more then 2-3 revisits. This keeps it quick. Also few revisits lets it remain fair. You could also give them one visit then force them to get to the back of the line. ;P
Sahara is a long visit. Players tend to have to talk to her around 10 times to get all 4 mystery rugs. Same thing for clothing shoppers. So, if you invite a lot of people. Then there is going to be a lot of players getting antsy. Some may try to push there way to talk or shop. So 1 player at a time is really good. 2 at most.
If you can for trades.
Set up a drop off spot at your airport. No one needs to wander off if they are trading.
Use fences to no only wall off important trees, stuff on the ground or flowers. You can also use it to block doors to shops. If people are there to buy Turnips, Talk to Celest or Sahara. Then keep them focused an not making side treks to the sisters for some outfits. ;P
Ask for names of visitors. If you invites a couple people at the same time. Get the names of who is coming. It is very rare, but someone might share a Dodo code. Or if your trading. It makes it easier to know who is coming for what.
Make a list! If you decided to charge for visiting your island for anything. Making a list on notepad or something. Can help you keep things organized. When every I open up for Turnip Buyers or Sellers. I usually charge a small fee (cause the price is really good). I usually get players wanting to visit more then once. So I get their names and number of visits and payments. I keep track of what has been paid an how many visits they make. It's really rude when someone comes back more then they agreed to and slow everyone down. When that happens I know to change the Dodo. I like to make things smooth and easy for everyone. I would hate to have to wait, so don't want to make others wait.
Final bit of advice.
This is your time. I here a lot of players go on that they feel wrong about charging for visits to talk to celest or buy turnips. That's cool. Just remember this is your time. The time you give up for these little visits and such is time you could spend doing other things. Your limited in actions with visitors and load screens. Do not be afraid to ask for something. Especially when you are offering something very popular. It's not greedy to at for at least a tip. It's rude not offer a gift to someone doing you a favor. After all. Every person that came to your island for celest, got something. A DIY or Stars. All you got was your time taken and maybe a smile for helping others. ;P
I hope this helps you.
Above all else though. Have fun!
Oh, for you post issue.
When it comes to stargazers. 4 is a good number. Set up a time limit. Say about 30minutes of star gazing. Let them all know this rule. Have them all send you a PM when they are at the airport rdy to come over. That way they are all synchronized. So they should arrive back to back. This will prevent them from interrupting the star gazing.

Lastly, when 30minutes is up. Give them all a chance to leave (couple minutes). Then save, end and restart he process for the next group. If not many people wanting to come. You can extend the time they can visit. 30 minutes is more then enough. You can go up to 7 visitors if you want. Just try to keep them grouped together. Again, nothing like having a group of stars start to fall. Just have someone show up late and ruin it.
