Same again. If a poll of 1000 has a MOE of 1% and one of 100 has a MOE of 10%, I am most definitely going to weight the large poll more heavily, no?
Then start a website that weights the polls. RCP doesn’t claim to do so. It provides the poll numbers, the links to the polling companies, and a simple average.
Mot necessarily. It depends on the quality of the sample selected. Did they get the 1000 from a diverse sample (likely voter, on the street vs phone, non-likely, registered, geography, etc) and the 100 from a controlled sample (registered and likely, diverse areas, etc)? If that is the case, I would weight the 100 sample more accurately.