When the wait time is few seconds, you can hold the brake while remaining in D. But since it could be tiring, so I usually switch to N when the signal is 1 min or more. For wait time of a couple of min, you can put it in P and turn off the engine like @mgalaxy3 mentioned.
Modern engines don't need to warm up like the old ones. Just wait 30 sec in summer hot weather and 1 min in winter. This is important to let the oil lubricate all engine parts. Don't wait if the engine is already warm.
Speed doesn't matter. RPMs matter. Drive under 2000 rpm when the engine has not warmed yet.
Almost all modern transmission don't have dipstick. They have fluid level check plug. You don't need to worry about fluid level until or unless there's a leak. CVT fluid level check is a lengthy procedure. I suggest not to do it yourself until or unless you have vehicle repair experience.
Make sure you change CVT fluid every 40,000 km or 2 years which ever comes first.
You can safely change between D, S, and L. But it's better to leave the accelerator before changing.
