My dining room is in between the other two rooms so I thought about putting the primary setup there and then running speakers to the kitchen and living room
Sounds like you are thinking of a single device running speakers across 3 rooms / zones.
That's not really the Wiim Way, although there certainly are products that can do this.
A classic Wiim Way would be something like one of their Amps driving a pair of passive speakers in the lounge, then maybe a Sound or Sound Lite in the kitchen and dining room, where you (or the better half) are more likely to want a smaller, less conspicuous unit.
No wires involved, unless you want ethernet into any of them, as they can use your wifi.
This would also allow you to play different music in each room, or the same music in any combination of rooms.
From the Wiiim lineup, I think the choice also comes down to room sizes and desired listening levels.
Personally, I don't think a single Wiim Sound is the right choice for a larger room, say 20m2 and above.
As for Pandora, I see that it's available in the wiim app, but I've no idea how it compares to using the Pandora app itself.
From the Pandora app I'd assume you'd have to either bluetooth or chromecast to a wiim?
For chromecast multiroom you'd have to use chromecast groups, not wiim groups. Chromecast is not gapless if that matters to you.
Feel free to ask more quesions!