Some ideas, some things we did in our own barn when we built it...good and bad, wish I had...
First one is if this is a metal sided barn and metal roof...insulate that roof to reduce noise from rain and dripping from condensation buildup. Today they can do blown-on and adhere to the roof itself or add rigid panels easily.
Our barn has a metal roof and no insulation nor sheathing under the roof and deafening it is when it rains hard and my horses get dripped on if they spent the night in stalls and morning sun warms the accumulated condensation moisture...drip, drip, drip on them and everything else.
My barn is a pole barn with openness not closed up side walls either.
Second you refer to feed/tack room...put a roof in it, enclose it and concrete a floor in it to keep down filth or pay for that every time you reach for anything. A fine layer of dirt, dust gets on and in everything...feed, hay stores...tack.
Stalls, use pressure treated lumber only. Horses urine and feces are caustic. Termites are attracted to untreated lumber and are in every area of the North American continent...that be you.
Barns are a huge investment...protect it.
So, my stalls are 52" high solid plank walls.
A combination of 2x6 and 2x8 to make this height used.
Our stalls are 12x12 boxes so we placed wall support every 4' in every wall for strengthening...my barn has temporarily housed a Percheron who had a kicking fit and did not move a wall nor stall wall boards...
We then have livestock panels like you find at Tractor Supply for the top stall section. Combined wood & panel stall walls are just over 8' tall.
My husband made a wood frame to support the panels so they fit tight and not move. He drilled holes where each wire end touched the frame, inserted wire in and then used a small metal bar he fabricated and screwed over the top, bottom and interval sides to double secure the panel wire from being able to be moved.
Panels allow air circulation, cooling breeze to happen but the horses can make ugly, ugly faces at each other but not touch.
My stall fronts are also made this way so my horses if restricted to their stall so they eat their meal in peace and the other horses are loose...no one touches them and steals or bullies them.
My stall doors are gates, wire filled so no hoof is getting trapped unless you have a mini.
We intentionally chose wire-filled gates again for the air circulation since we are in a hot & humid awful location. My horses can all hang their head over their gate/door and see but not touch their neighbor because we designed our barn as such.
Our doors open into the stall and flush to the wall so when pinned open they take up no room.
Plus is you have to have a very savvy horse to figure out to open and get out if inside, downside is if you are in and need out in a hurry you must get around that gate...however over the top is also easily accomplished!
Make your design so you can hang 2 buckets for water and still have space between them and where the feed tub will be if you have hung feed tub/buckets. I use large floor pan feeders myself.
If your barn is metal sided, please cover the walls at least 4' high, make a kick-wall to protect your horses from severe injury if they should kick a wall or roll and a hoof fly getting up...de-gloving a leg is a terrible injury.
Encase all electrical wire in solid conduit so no vermin of mice/squirrel chew and create a fire danger.
Plenty of outlets as extension cords are not the safest in a horse barn atmosphere.
If you plan on stall fans wire during construction for outlets/plugs high in the walls and only use enclosed motor fans to reduce fire risk from dust/dirt accumulations.
Water spigots that self drain are a must in cold climate and frost-free hydrants deeply placed so they indeed not freeze.
Some things we found doing our research and build...some I wish we had done, some I worked in barns and learned firsthand pro and con of....
Enjoy your fantastic project, and please share pictures along the way of reaching that dream.