I'd shut off the door to garage/car port if not used, leave the doors into LR if possible - are they glass to let more light into the 'unsun room'? if not, I'd put in glass doors, and put sheers on the sunroom side. put in a skylight, close off the doorway into the kitchen and make a doorway into DR (where windows are now). and use the sunroom as a TV room study/office, computer room??? then in DR you'd have a partial wall ( along sunroom side) to put shallow cabinets. pantry cab? hutch with glass doors for dishes? I'd keep the kitchen where it is to see out that window into backyard (I love that myself). I'd keep the sink where it is - put as much window over it as possible - no upper cabs over sink wall. on the turn from the sink to the right I'd run cabs with stove toward the end of that wall - and if you really need a peninsula area (for dh to sit and talk to you while you cook - or you to talk to him while HE cooks) just put a nubby one at the end there part the stove (coming off of what is now door to sunroom and). put the glass doors (maybe not sliding tho) to the left of sink area/counter. on the other wall (counter and fridge now? I can't read the wording on the LO - bad eyes) I'd put a counter depth fridge with a bit of cab/counter on either side of it for a landing pad. another possibility would be to swap the stove and fridge - setting the fridge back into the ? area in the sunroom. then you could also look out the back glass door while cooking. tho I think I'd like the fridge more on the other wall - out of work area (in case dh/ someone wants a drink/ice etc while I'm cooking) - and so dh could sit at counter top and talk to me. I doubt dh would be sitting there to talk to you while you are taking things out of/putting into the fridge - lol!

If that's to scale, there is no way that there can be even 6 feet of headroom in that loft unless that rendering is waaaay out of scale. And how do you get up there? Where will the stairs be? The bathroom door swing is impossible. The post is in a horrible place and would be completely unnecessary if engineered correctly (using the bedroom wall for support or a small wall at the kitchen cabinets, etc.). That house looks like a maximum security bunker with all those mimsy little windows with slits for the guards to look out of. Even on the north side of the house (which gets no sun), the windows are skimpy. That place will be a cave if you don't open it up a lot. Do you have a real view in any direction? Maximize it. Look at other houses, and look at house plans. There are basic, basic flaws in this layout. A small house needs to maximize space, and this doesn't do that. Your idea of "extreme temps" is skewed. Philadelphia has 10-20 (and lower) winters and 90-100 humid summers, and we use all the glass we want. You do not have extreme temps, by any stretch. Even my 100-year-old house has at least two 12-foot-square (or larger) windows on each exterior wall in each room on 3 floors. Don't be afraid of windows.

Concerning the master bath. You could keep the fixtures where they are and just replace the vanity and add another across from it. You could move the California closet to opposite side and create a hallway into the bath which gives you more wall space for a second vanity. Keep the tub and shower. Save plumbing cost. Concerning the new bath addition. Be careful you have enough room for a toilet across from the vanity in the new bath. Maybe a pedestal sink across from a small toilet in a shorter length. Your layout seems tight. Even in my drawing with a pedestal sink, you may have trouble clearing the sink when you open the door. I put in a corner shower, but if you can fit a tub, that might be better.

I'm afraid I don't fully understand the plans. Where is the window in the little eating area (below the AC, beside the one sad red chair)? My first thought was what about a kitchen with no upper cabinets? You could run lower cabs / countertops right to that half wall above the living area, getting rid of the "bridge" of upper cabinets. Maybe a shallow pantry cabinet on the load bearing wall, and possibly shallower cabinets opposite it as well depending on the aisle space available.