Replacing swamp cooler pads

The optimal CFM is related more to the cooling capacity than house size, since you have low pressure (usually the other major factor). The cooling capacity is related to house size, climate, and many other factors, so there is some indirect relationship. I couldn't tell you what that is. Consider this a verbose comment and not an "answer".

For the bedrooms to be adequately cooled with that setup, the living area would need to be colder than normal, assuming the unit is adequately sized for the whole house. On the average, your house will be kept properly cool, but you will find the temperatures will vary noticeably from room to room. Neither extreme may be all that comfortable.

That looks like an Adobe P2-911 plug and it is proprietary. There's another version Adobe made (I believe it's for the 230v motors) that has a 5th round pin. The flat bladed terminal is for keying the connector so it can't be plugged in upside down. You should have a 115v cord with 2 hots - one for high speed and one for low speed, 1 neutral, and 1 ground.