A trick is to know which brands you need. Marriott's Residence Inn is a big reliable one (for multiple "rooms" and kitchen/laundry) that exists almost everywhere in the US. It's a part of the whole Marriott system and often in tourism lulls in various cities has deals that keep it comparatively well priced with other Marriotts in that city and will let you use Marriott points to further defray costs.
Hilton and IHG both have similar brands, but their exact names escape me at the moments. The search keywords are "extended stay" and "apartment hotels".
Depends where you are. Maybe in expensive cities where space is at a premium. But suite hotels (with various levels of kitchenette/kitchen) in the US are not, in my experience, notably more expensive--though often have simpler facilities--than more conventional hotels. (Bedroom may not be actually a different room from living room area but is often at least somewhat separated. So may not help with kids. Stay in this type of hotel in the US a lot.)
Just having a separate living room and bedroom in your hotel can be hundreds more per night.
Interconnecting rooms are rare, you can request it, and it’ll be subject to availability. So you can’t even guarantee you’ll have one.