I am have an October use year and absolutely love it. I like to travel in the last quarter of the year typically because of the heat (I am from Michigan). However, with that said, over a 12 month period from April 2018 to April 2019, I will have traveled in April, July, October, November, December and March. If you know you are going to book your vacations in August, try to lock in a week that you want. But you also have until May 31st to bank your points if needed. For me, that 4 months isn't an issue because I plan most of my travel at least 6-11 months before hand. But as you enjoy your membership, I am almost certain that your travel preferences won't always be in August. You will want to experience Christmas and Halloween, Food and Wine and Flower and Garden at some point. So from an October user year person, I don't think this is a bad decision to have that use year. It has worked out great for me. In fact, I have added on 5 times. I looked at resales with other use years and have always chosen to have an October use year.
Just remember, UY has nothing to do with when you plan and when you book. It really has more to do with banking deadlines, and what points will be available for when you travel, not when you book, and what to do with points if you have to cancel. Traveling later in the UY, no matter when you book, is risky if you have to cancel. With an Oct UY, points from any trip booked for June to September, if canceled more than 31 days out, after May 31st, will need to be used by October 1st of that same calendar year since one would be beyond the banking window.
If you have a specific time you know you will travel, getting a UY that allows you to travel within the first 8 months, gives you extra protection to still be able to bank points if you cancel. Of course, if one travels all times during the year, some trip will be vulnerable in this situation.
For OP, traveling in July/August, with an Oct UY simply means that if you ever had to cancel that trip...at least 31 days in advance...less than that they become holding points and a whole bunch of rules apply..after May 31st,your banking deadline you will only have until Oct 1 to use up points used for the canceled reservation. It doesn't matter if you booked the trip 11 months in advance or 4 months in advance. Once you pass your banking deadline, any and all points in that UY at that point must be used.
When I bought in, we traveled in August as well..I teach...so we bought a June UY because if I did have to cancel, I had plenty of time to still vacation. Fast forward, now I am one year from retirement, plans have changed and I now travel many different times of the year. So, as I added on points, I chose different UY to ensure that when I book my reservations, I use points with the least risk if I have to change/cancel...which I have had to do a few times!
Good luck with ROFR!!!!