Okay, I am Officially Frustrated!

I was in the exact same situation as you were for my first tri last year; in fact, it was also a 400m pool swim.  There is nothing wrong with stopping at the end of the lane to catch your breath.  Move to the side of the lane opposite where swimmers need to go under the lane dividers to cross over.  Take a few deep yoga breaths and then conquer the next length.

I ended up doing half the swim freestyle, and resorted to backstroke for the second half.  Nothing wrong with that either.  I saw people doing sidestroke, in fact.

Just try to relax as best you can, and focus on your breathing.  You'll do it.  Good luck!! 

If you are at the end of the line, you will be with other swimmers who also struggle, so do whatever you are most comfortable with. You won't be the only one resting on the wall, nor will you be the only one doing other strokes. Get through the 400 in the way that is best for you.

Oh yea, and whatever you do, have fun!

Do whatever you need to do in your first race and don't feel bad about it.  Most who have struggled with breath issues seem to say it's because they don't breathe out enough, but you can work on that as time passes.  Try to stay relaxed during the swim and focus on the fact that you'll soon be out of the water and doing your stronger legs on dry land.

Have fun.

Since your going towards the end of the line on race day you will feel much better about resting at the end of each 100.  You will be watching everyone swim and you will see that happen quite often I'm sure, Some may rest only a sec or two, others a bit longer. Even without me knowing what race you are doing I"m pretty confident that you will see enough people resting and breaststroking that any worries you have about that will taken care of.. Just remember there is the extra energy of the excitment of race day which is not nervousness..   Relax,, have fun,, finish swim and go out and pass people on the bike and run

Yes

Did you estimate your time well? If so you will be with others swimming similar pace. I think you mentioned in a previous post you put a really long time down...so  you will not have to worry about blocking others in.

If you can keep moving forward and not resting that will be faster. When I did my first tri in the pool which was my 2nd ever, I felt very anxious so I did what we learned in TI and did sweet spot kicking on my side with one arm in front of me. I made forward progress but didn't stop.

You have 8 days, next swim see if you mix up your stroke you can do 400 without stopping. If there is a lane next to you empty try getting to the end of the lane and pushing off under the lane dividers as that feels a bit odd too.

Best thing is to stop at end of the lane or change strokes and if at all possible don't stop in the middle of the pool. 

No matter what enjoy your first tri 

The exact same thing happened to me a couple of months ago.  I find that if I can get through that first 100, my breathing starts to even out and my stroke actually get better.  Now I can easily do 100 every time.  The challenge for me is to work beyond that distance so I don't get stuck in the mindset that it is my limit.  My coach gives me days of short sets and days of longer sets.  Those freak me out a bit, but keep my moving in the right direction.