We did our 2nd floor laundry about 5 years ago. About the same size as yours.
We have top loaders, so not the same concerns as the higher rpm front-loaders.

My recommendations are to install a nice bathroom-type fan to run so your bedroom won't smell like bleach or detergent.

Good lighting.

Enough electrical and floor space for an iron and ironing board with convenient electrical outlet.

And hanging closet rod for hanging up clothes from the dryer. And floor space for a "clothes horse" to air dry sweaters and such.

Ours was also a new build-over our 4 season porch. We did 2 closets, laundry/dressing room, and office. I don't know what your Master Bath situation is. Our home is from 1931 and our bath is tiny. So now I use the bathroom to shower, but do my makeup and dry my hair in the laundry/dressing room. This has been really great. Like having his/her bathrooms almost. So we have a basic 5 foot length of formica counter with a small but deeper type of SS laundry sink in it at one end. We used basic grade unpainted kitchen cabinets, which were painted white. This give fantastic drawers and under sink storage. My drawers are actually big enough for my hair dryer and hair products. We have a large mirror and vanity lighting, as well as ceiling can lights. Also put in a medicine cabinet on the end wall for more storage.

Geting back to your construction questions, our code did not require floor drains. Our machines are standard top loaders and don't have the RPMs when spinning that front loaders have. So our floor is engineered for the weight but nothing special beyond that. We did have architect/engineer on our build.

Good luck.

Be advised that 5' is not very wide for a laundry room. Our house originally had a first floor laundry room that was about 5 1/2' wide and 12 feet long. The w/d were at the far end of the long wall. It was awkward getting the stuff out of the dryer: you couldn't do it from in front of it, you had to kind of squat in front of the washer and reach over to pull the stuff out into a laundry basket. Hated it.

We built a new laundry room on the 2nd floor. We didn't do anything special, just have the washer in an overflow pan with a drain to the crawl space, so I can't help you out much on that end.

Drain pans under washers and protection from broken hoses (Watts has one system).

since it's a new build perhaps you could specify more about the structure, joists etc.

since these are new machines you may be fine in terms of anti vibration.

ideally, a floor drain has a "primer" that gets water from another source regularly.
If not, you have to fill it up from time to time.
This is a pain in the butt because you only know about it when it's too late (the house gets sewer gases).

h th

I have strange issue. Installation guy said I need washer pan 34 X 31( Internal 33X 30). This is for GE FL machine. I cannot find pan of that size in all home depots. max I got is
32 X 30 external ( 27X 30 int). Please advice

"If not, you have to fill it up from time to time."

Without a trap primer it is unlikely to pass a code inspection.

Using the washer cold line to prime may be acceptable to the AHJ.

There is a product called FloodSaver that comes in a model deep enough for your application. And their surround product is nice since it runs up behind the washer in case of a burst hose.

To avoid the sewer gas issue I was advised to pour some mineral oil into the trap. It doesn't evaporate.

Here is a link that might be useful: FloodSaver

While mineral oil can help prevent evaporation from the trap, it is not a code compliant solution.

A trap primer is.

We actually put the overflow pan drain going straight into the crawl space. No p-trap--not needed because it's not hooked up to a sewer pipe. We okayed it with our inspector before doing it.