1. “First visit” is no different than any other day you use the pass. There is no special treatment for the first visit. So look at the Flex Pass calendar and see if the first day you want to use it is “reservations required” for either or both parks, or is “good to go” for both parks. If a reservation is required for either or both parks you want to enter on your first day, you won’t be able to make that reservation until you purchase the Flex Pass (which may be before your first day of use or on the first day of use, your choice). Some other AP types have reported getting a free “day ticket” to enter on the day you buy the AP, even if that day is a block out day. To my memory, no “day tickets” have been issued for Flex Pass buyers on day of purchase, and several people have reported having to make a reservation for that day right upon purchasing the FP that day, since the day was “reservation only”.
2. People have reported that all of those dates have been given to them as the start date of the pass. The correct start date (we think) is first use, so if it is anything other than that, you will have to go to GS to try to get it fixed (exception is that if you use a ticket, then upgrade the ticket to the FP before the ticket‘s last day, the start date for the FP will be the first date that you used the ticket that you are upgrading to the FP).
3. Every DAY that you want to enter the park(s) counts as a unique reservation. So if you plan to come for 5 days and all 5 days are “reservation only”, the most you can reserve at 30 days in advance would be the first two days (or the first day of your trip and some other day of the 5 days). Once you scan in (most have reported) the first reserved day, you can book the next one. At any given time, you can only have 2 individual days reserved. So for a 5 day trip that is all “reservation required”, you would make 2 days reservations at 30 days out (or whenever you can before the trip), then make the 3rd day after using day 1, then make the 4th day after using day 2, and make the 5th day after using day 3. So yes, you are making reservations throughout the trip (if they are available, which is a risk). If some of the days of your trip are “good to go”, you won’t need a reservation those days, which can really help the uncertainty.
4. The max number of days you can RESERVE is 2 in a 30 day period. They do not have to be consecutive. And if some of your trip days are “good to go”, you could string together a multi day trip and only need the 2 reservation days. If your trip encompasses more than 2 “reservations required” days, you will take the risk that those days may not be available to reserve after the first 2, while you are on the trip. This is why the FLEX in the Flex Pass requires YOUR flexibility to either focus your trip on mostly “good to go” days, or be flexible enough to not be able to get into either park on short/no notice if there are no longer reservations available for your dates.
Long answers, but hopefully helps you and others understand this unique AP.