500 should be a little over for AKV Savannah and a little under for Aulani OV assuming 7 nights during the summer since this is Magic Season for WDW and Premier for HI. It'd be premier for WDW for easter. That's assuming 2 BR but if you were OK with a 1 BR (pullout plus smaller pullout sleep 5) then it'd be a little less. It really depends on how flexible you are within the school calendar and ho frequently you are likely to go to each. Assuming every other year at each and that you're well versed in all the WDW resorts but set on AKV almost all trips, my first thought would be to buy 2 contracts, one at each of at least 250, probably a little more. Resale that's roughly $100 per point. I'd also make it a priority for Aulani to find a subsidized contract. You'll pay a little more up front but end up far better off long term. And I'd suggest you consider one and see how it goes. You might also want to look at non DVC for HI which will give you more a lot more options and likely be cheaper still long term.
The best UY is the one that starts just before your usual trips, if that's summer, June is likely best but for Spring break March is likely best. And it may be the retail perks are worth it in your situation so you might buy resale then do a retail add on of 75 pts for the perks. With the pass discounts you might be able to make up the difference in a few years depending on how you used it. If you don't have enough DVC experience/knowledge for the various resorts buying just SSR will be cheaper still both short and long term and should get you in to those options routinely but cannot be guaranteed. That's esp true if you are fairly flexible and/or want to try multiple resorts over time. SSR should offer modest up front savings but it'll save you almost $1 pp over AKV and over that on Aulani non subsidized. At this amount of points I would buy 2 separate contracts even if the same resort but personally I'd give myself options.
