when staying on points, how do you purchase advanced tickets to WDW? I would like to get the tickets at check in at SSR. Do I call MS or CRO or another number?
I believe you can order advance purchase park hopper passes on line at the WDW site or buy them at the Disney Stores. The online takes a little doing because they steer you towards buying a package, but it can be done.
UPH (Length of Stay) passes cannot be bought in advance if you are staying at a DVC resort on points. However, if you are a DVC member, you may purchase UPH passes for a 10% discount (off the gate price) at check in. This is a better deal than the advance price anyway, especially since the CMs will allow you to drop the day of arrival or the day of departure and sometimes, both!
There are no "restrictions" on buying any other type of ticket that is available to be purchased in advance.
If you do not want the UPH tickets, check out some of the other reputable (non-Disney, but authorized to sell Disney tickets) ticket brokers (including the DIS). Many offer better prices than Disney's advance purchase prices.