Here are a few basic questions I have now that I am doing some swim workouts-
1. How to do flip turns. I never learned this and it does seem disrupting to pause at each end of lap (though sometimes I welcome the stop, turn around, breathe and go again...)
This is a big question. I'll try to be brief. As you approach the wall you tuck and summersault just in front of the wall. It's best to blow out through your nose when you tuck and roll, this keeps water from being driven into the nasal passages. Imagine you have tucked and rolled 180 degrees. Now, your feet are supposed to touch the wall (with knees bent like a squat) while you are facing upward, belly toward the water's surface, with your arms stretched out above your head in a streamlined position. You push off the wall with your feet from this position and twist back into the normal freestyle body position after pushing off the wall. It's that easy.

My coach used to have us practice this over and over at the shallow end of the pool for 25 min at the end of a workout. You stand far enough away from the wall to get about 5 strokes in before you turn, then push off and try not to have to stroke or surface before hitting the backstroke flags.
There are a lot of very fast people in triathlon that do open turns at the end of the pool. These can become very fast as well if your timing is good.
2. What is a typical time for a 400? Or even one length of the pool (25 meter/yard)?
That varies a lot. A good swimmer (ie someone who started swimming when they were a tyke and kept it up) can do a 400 in under 5 min. I'm a decent swimmer for someone who started in adulthood and my best 400 time was 6:25. Most people new to the sport will not crack 8 min for 400 until they have a few training seasons under their belts.
3. Does anyone sidestroke or breaststroke in tris, if for nothing else than a short break from freestyle?
Yes. Especially in tris with a pool swim. There are a lot of people who will choose these for their first tri and I have seen many people breakup the swim with other strokes. I have not seen anyone do this in a race longer than olympic distance.
4. Lap counting. I lose count easily. I think coaches use little metal counters but is this something you swim with?
Lap counting takes practice. There are not lap counters that I can think of for use in the water. I try to associate a lap with a body part to help me keep count. Eg, I'm swimming a 400, each 100 will represent a limb for me, one arm then the other, one leg then the other, then I'm done. If I'm swimming 500 I might count fingers. You get the idea.
There are others, but that's enough for now... thanks.