You have a good enough rough opening and may need it depending on how square your opening is .If the opening is square or close to it I would nail a 1X on each side and shim to make it square.Your casing will cover the gap at the top so no need to add.The 1X on each side will still allow 1/4" each side to shim the door jamb.

Electric water heater, yes? I don't see how bypass doors are going to work with this situation. You will need three doors (32" doors) and a cased opening. This opening does not appear to be a typical 2x4 framed opening. You need the depth of a traditional casing in order to mount the track to the header. The track(s) will be a lot wider than bifold tracks because each door slides in its own track. IOW's, you will need three tracks mounted side by side to the header. I have bypass doors on three closets in my house. I so dislike them. I don't love bifold doors either but bypass doors are much, much worse.

SO you each have a 7' x 13' closet? Outside a luxury sized bath? And more closets, un needed upstairs? You have a SPACE issue? Honey, I doubt it. You simply need to put OUT of season, upstairs. in season near the bath. Then call a California closet, or a Loews. ( yes.... they can do a nice job ) and together, with an ASSESSMENT of your cloting......sports, dress, folded, hanging, shoes, accessories, scarves, belts bags et ALLLLLLLL, You decide how you want to out fit the space. Thart's the shortest route, because clolthes are personal. If you tend a farm, your closet doesn't look like someone working o n Wall Street. The clothes required are different. If you can't find room for grooming and bath supplies in that bathroom? You need a major purge of who knows what : Maybe you need a make up table under that window. Only you know. Only you know your clothes. Maybe you're Sarah Jessica Parker, and maybe you aren't : ) You must "suggest....you" Lighting is dependent on ceiling height, and needs to be ether recessed or flush mount

All fair. I understand. When we moved from condo to house while I was pregnant with baby two it felt so glorious to have all this space suddenly but also not needed. If you are building this house to live in 5-10 years, then even in that time your wants and needs will change. So you want to build for flexibility. For us these were things we wanted as an example: When our kids were very young we loved having a small family room right off the kitchen so we could be in kitchen while they played. Now that they are older we have a “nicer” open concept main floor with living area but then a rec room in basement. For us kids bedrooms being near us has always been important. Making sure the bathroom(s) they access make sense. Having one bathtub for bathing is great. Making sure we have a guest room that feels private is important so family can visit. Large outdoor area for kids to play that is safe and flat and fenced. Lots of outdoor seating so grown ups also can enjoy. Many windows so we get lots of natural light. An open concept main floor that allowed for us to all be together and was great for entertaining. A mud room and laundry that were together so we could wash dirty things easily. Mud room well set up for storage of kid stuff. Did your architect ask you questions about your lifestyle and wants and needs? Have you looked at any homes you liked and considered why?