I’ve contributed to other threads on this topic several times in the past, so what I’m saying here is probably not new.
I LOVE the attached barn/house concept, and it’s very popular where we are.
My notes on your plan:
If you eventually plan to build a “real” house, I’d probably prefer a huntbox (living quarters on top of the barn), but if you’re set on single level, then I’d do the barn in “front” and put the living quarters in the back. Then when you eventually have the real house, you’re not having to go through empty space awkwardly to get to the horses every day, and if you rent it, the renter isn’t ‘front and center’ on the property, if that makes sense. If you don’t intend to rent the space when you’re done living there, try to design the space to serve as dual purpose for whatever you would want to do with it.
Another option would be to just plan to keep the attached apartment as your main “real” house. If (probably) budget constrains prevent you from building large and perfect (thus the intent to eventually build a second home), then maybe instead design it to serve as part of the ‘real’ house, and build an addition to it later. Have a plan for the eventual footprint and design the smaller piece to fit with that plan.
I will agree with Soloudinhere, that proposed house size is TINY. We rented a place (attached to a nice 3-stall center aisle) that was not much bigger than that. I swear we almost got divorced because of it… TOO SMALL. Even with a rented storage unit in town, we never had room for guests, or for private space, or even storage of all our stuff. I would try to make the living space a little larger, even if it means waiting another year or so to save up.
Other thoughts:
think about storage solutions. A small house and a small barn will both require a lot of “stuff”, and planning ahead for that will make a huge difference.
The mud room between the two spaces should be a little larger than you think. you’ll have different “sets” of clothing: barn boots, going out in public boots, barn coat, barn rain coat, barn warm coat, and then equivalents that are suitable for going out in public and being seen and smelled by non-horse people. DH will need all those versions too, so again, plan ahead for maximizing space. I can’t imagine trying to fit all that into a tack room. I have a generously sized tack room that is also used for feed (grain only) and it’s FULL, with a ton of overflow of tack and blankets in boxes in our house.
Like all barns, attached to houses or not, put a lot of forethought into drainage and mud management (and snow management if you live in a northern climate). Also where will manure be stored? hay? Shavings?
It sounds like you’re not planning on starting this for several years, and priorities and situation can change a lot in that time. But it also gives you lots of time to plan, get grass established, walk the land in all seasons and after hard rains and kind of get to know the property. Good luck!