Feedback/advice on traveling to Chiang Mai / Laos / Vietnam [closed]

Three of us (my wife, 9-year-old daughter and I) are planning to visit Northern Thailand and Vietnam in Nov-Dec. I've done some research on the trip and would love to get feedback on the plans. Any and all advice will be very much appreciated too.

DURATION

We'd love to spend 2-3 weeks traveling. It seems that flights (from Seattle) are a major expense but staying there is relatively cheap. If true, then would lean towards staying longer.

Besides transportation, I'm planning on average of $75/night for lodging + $50/day for meals.

Is this reasonable?

ITINERARY

We will be flying from Seattle, WA. Given that we will be traveling with a child, flying for 20+ hours might be challenging. So I've looked at flying direct SEA -> ICN or SEA -> TPE, staying there for a couple of days and then flying to Chiang Mai.

Are there any other hubs I should be looking at?

I'm trying to strike balance between seeing multiple places yet spending less time on transportation itself (unless it's scenic or something).

I'm thinking of spending 5-6 days in Chiang Mai and exploring both the city and countryside. Would love to spend time in one of the Elephant Sanctuaries.

Should I bother renting a car or taxis are cheap enough/readily available?

Since we will be 'in the area', I'd love to visit the neighboring regions/counties. One option is to fly to Hanoi and spend time in Northern Vietnam. The other is to visit Laos but I'm not sure how safe/comfortable it will be there with a child (I do like that it seems less touristy). Myanmar is also pretty close but I'm worried it would be difficult to get around speaking English only.

How necessary do you think are local guides there?
I've never hired one so I'm not sure how much it costs, but if it will help enrich an experience, I'd be up for it.

Anyway, I'd love any feedback/thoughts and pointers on this. Thank you.