Buying resale is more complicated than buying direct retail, but could save you a LOT of money up front. Currently, DVC is selling CCV and Aulani. While CCV is a lovely resort, it's not necessarily the best choice for everyone. You have children who are 10. When CCV expires, they'll be near retirement age. BRV, also at the Wilderness Lodge, expires in 24 years. They'd be in their 30's. BRV resales are typically under $100 a point, so just under half the price of CCV. While it's technically cheaper, per year, to buy CCV direct than BRV resale, that only works if you intend on keeping the contract until the end. Often, we see people selling their contracts in 10-15 years, as children go off to college and their first careers, and the parents decide to travel elsewhere on vacation. Resorts with longer expiration dates work well if you're planning on selling in 10-15 years, as they will still have considerable value compared to a resort expiring in 10 or fewer years.
If you want a 2 bedroom dedicated in the MK area, BLT, GFV, BRV, and CCV are your choices. BLT (my home resort) has the distinction of having a walking path right to the MK. It's also got low maintenance fees, many dedicated 2 bedroom units, and an end date 42 years from now. GFV is significantly more expensive per point, fewer contracts being sold, higher maintenance fees, but it is The Grand Floridian (so, yes, really that nice). Other options with longer expiration dates are AKL and SSR. Both of these are bus-only transportation to the parks, but absolutely beautiful resorts with many 2 bedroom dedicated units. SSR is consistently rated the best DVC value due to the low resale price (for a resort expiring in 37 years) and low maintenance fees. The only 2 bedrooms at the Poly are the bungalows, which require nearly 2000 points for a week long stay.
The mantra for high season (September through mid January) visitors is to buy where you prefer to stay, or at least where you wouldn't mind staying. If you're not a risk taker, choose a resort and buy there. If you're a risk taker, you could buy a a cheaper resort and attempt to book at the 7 month mark. Often, you'll hear SSR owners tout this strategy, which can be effective or a complete frustration (there are long threads here on disboards about how hard "it has become" to book at 7 months).
Use year determines when your annual points are given to you. If you are normally travelling in September or October, you'd want a use year of August or September. The reason you do this is to allow you to be able to bank points that would otherwise be lost if you had to make a last minute cancellation of your normal September/October reservation.
I encourage people to rent points for a stay to see if they like the resort they've chosen. While it's a little late now to book a September/October 2018, if you're not in a hurry to buy, you could stay next year. Begin your planning by contacting a broker about a year before you want to go. That way, the broker may be able to line up an owner with the correct number of points to book exactly at 11 months.
In the mean time, consider how many years you are likely to continue to go to WDW, how much of risk taker you are, and which resort really is "the one" for you.