I'll share our experience. We've had very good luck with Flights by Celebrity (Formerly Choice Air). However, there are a few quirks to be aware of to avoid some issues people have complained about on CC. What airline did you end up booking? Are you flying on that actual airline or are you code sharing?
1) Yes, your pricing is safe and will hold even if you don't pay now. However, chances are you may not be able to pick your seats until you pay in full. This has at least been our experience flying AA, even in first class. Once paid in full you can choose your seats. But as stated previously above this can vary depending on your airline, however, most, regardless of class, will not allow you to choose your seat until your reservation has been fully ticketed, meaning they've received payment. But don't let this scare you. Your fair is still safe!
2) The great advantage however is not having to pay right away until final payment. I would look at your airlines seat map for your flight directly on the airlines website to see how booked up the cabin is. If it is not that full then I'd wait on paying until July 2nd. However, if it looks pretty full and only a few good seat pairings left then I personally would pay now to choose your seats. However, this is assuming you cannot choose your seats now.
2a) - Choosing seats might be tricky even after booking depending on the airline. Usually you can choose them directly with the airline, but in some cases you may either have to use a specific link from the airline (because you booked through flights by celebrity) or you may have to contact Flights by Celebrity to choose your seat.
3) Add your flight confirmation to your frequent flyer account for the airline. If you don't have a FF account for the airline then get one and add your confirmation number. One thing we noticed is that booking in advance you might have equipment changes or flight time changes. Flights by Celebrity has notified us of these changes and they have also not notified us of these changes. However, if you have it linked to the airline frequent flyer account and have alerts set up you will be notified immediately by the airline.
Sorry for rambling. Hope this helps!