Multiple questions thanks in advance Options

[Oreo20]

Straight forward I have a couple questions answer if possible thanks guys

1. I’m about to replace the passenger Cv axle I’ve never done a transmission flush will doing so now
After 204,000 miles be bad is it ok to replace oil ?

2. What could trigger the car to have a shaky idle randomly
When I stop at a light it only happens sometimes steady rpm and out of no where it drops like it wants to shut off

3 is it normal ? I took out my spark plugs to see overall health and they are white/ grayish tip
With tip still being like new changed 10k miles ago

Thanks for the help

[narly_charley]

You almost never want to "flush" your trans at a shop, especially with high mileage. You'll want to just drain in your garage and refill. Do that for the next few engine oil change intervals and you'll be good for a while (probably the life of the car/trans/engine) IMO.