Friends trip: Milos-Paros-Athens in September

September is not July, but about 8:30am, I bought my combo Acropolis ticket at the ticket booth with about a 5 minute line. (It was probably a little longer later.). The ticket line at the Museum might have been nearly that long. Neither was bad, but if you can buy them ahead, there’s no real reason not to. But there’s also no reason to pay a third party fee, either.

Good plans! And thanks for all the pertinent details; it really helps us in giving useful advice. Here's a good map I've found useful in helping Milos plans -- https://www.seakayakgreece.com/virtualtour.htm My thoughts:

MILOS BOAT TOUR -- In high season, there seem to be big vessels, 50+ passengers, sort of "party boats" - but not in off season, late May when we went & Sept for you. Boats line up in Adamas harbor before dinner, u can walk along, go aboard, ask questions of the skippers &decide (and YES, it's a good idea to wait til day befoe u plan a sail & get the weather forecat before committing). 2 types of boats; small sloops, 6 psger, and larger catamarans, capacity 12-15 psgr. 2 types of trips -- around whole island, or go to Kleftiko -- which and then retlurned. (For hi season, I've seen 3rd version - goes past Kleftiko to Provetas beach, passengers get off, met by a bus... but not seen listed after August). Two from our group went on a sloop, hoping to crew, but it was so windy it dropped sail motored the entire time... and circled whole island, so almost no time to stop for swims & bbq. Three of us chose large catamaran "Chrysovandu" (14 capacity, but only 8 that day) It was able to go under sail 70% of time.. also we went to Kleftiko & back, plenty of time to stop for swims & a beach picnic. We had a great time, recommend highly. Remember, Sept can be a windy month.

MILOS TRANSPORT -- ATV's sound good, during day, the best way to get to beaches, Milos bus service is very limited, About Chora, the road IS steep... there is a bus that goes there several times a day, just have to time it... and you CAN walk down, good walk. I stayed 2x in Adamas, when I was solo, with no car, because most restaurants & (low-key) night life is there... only about 2-3 restaurants n Pollonia. Third visit, car with 5 of us we stayed in Pollonia, had dinner in Adamas 2x A number of us really like wine with dinner, but luckily we had a teetotalling driver... Island roads re twisty and NO lights on roads. MILOS RESTAURANTS - never heard of reservations. My recommends wouldn't be current; others will know better.

LUGGAGE STORAGE - u could do just what I did, googled Parikia Luggage storage... there's an internet cafe that takes bag but the only review is a neg. Santerineo Travel Agency stores luggage, right near port, good reviews, seems a better bet.

There are water taxis that meet the ferry at Paros town warf. They go directly to Antiparos but depart shortly after the ferry arrives. You will have to be fast getting your bags stored. Of course you can take the bus to the ferry which crosses to Antiparos on a regular and frequent schedule. Good plan to visit Antiparos.
Here is what it is like https://www.flickr.com/photos/stanbr54/albums/72157632126687570

As Janet says on Milos the boats line up at the harbour in the evening so you can tour the ones that interest you. We chose a smaller sail boat that could take 12 people. It had 8 on the day we went. It was a half way around the island with a long stop at Kleftico for swimming and a zodiak tour of sea caves. I think the half trip while we saw less gave us time to appreciate Kleftiko. I am pretty sure all the boats offer food and drink. It is a fairly long day with mid morning departure and early evening return. While the food was pretty ordinary there was lots of it.
I highly recommend you visit Plaka for sunset. Honestly the sunset views from Plaka are as good as Santorini and are not crowded at all. There are a couple of great tavernas in Plaka our favourite was called two doors which was the translation of the actual Greek name. If you drink you might want to take a taxi back to your hotel.

Milos https://www.flickr.com/photos/stanbr54/albums/72157634779985764
Milos 2 https://www.flickr.com/photos/stanbr54/albums/72157632109429236

My experience for the Acropolis is get up there a half hour before opening and buy your multi site ticket. You will b e there for the opening ceremony and will have a hundred or so other people around. You will have a full hour before the tour bus crowds arrive. That when you might want to depart and visit several of the secondary sites. They will be fairly empty because the crowds will be baking up on the acropolis.

4 nights in Athens is Good amount of time to visit the sites and to really explore the area near and around the Acropolis. There is lots of interesting neighbourhoods and of course don't miss the hike up Filopappos Hill with its amazing view of the Acropolis.

Athens https://www.flickr.com/photos/stanbr54/albums/72157632121475515

Have a great trip

Apologies for the delayed response - I've been without wifi for the last week or so, but thank you all so much for your thoughtful responses. Truly appreciate all of you for taking time to respond. I'm getting a little more nervous about Delta these days, but fingers crossed things will be okay and we will stay safe.

Thanks again!