One piece of advice to make sure you get the dates you want with little downside risk of having to redeposit your miles when the return leg's not available.
Book your outbound leg on the very first date you can (normally 329 days out). However, adjust the booking date to permit an immediate return flight (so probably 327 days out from the outbound flight). Then, rebook your return flight on the very first date it comes available. Whether the return is two weeks or two months after your outbound flight, this technique should get you the flights you want on the dates you want them. As insurance, make the res at the first possible moment on the day you can make the res.
Unless you use this technique, you may well be out of luck when you go to book your journey in peak travel months since while your return flights will be available, your outbound flights will already be booked up at the mileage-saver level.