OK, there are a lot of things mixed up here.
1. It is perfectly reasonable -- and necessary -- to want the two of you to have time together, both as a family and as a couple.
2. Your DH has different passions than you. You appreciate his passions when they are applied to things you value ("growing" your own nuclear family), but not when they are applied to things you don't value (growing non-humans).
3. You value certain things more than your DH (cleanliness), and you resent when he does not sufficiently prioritize those things. You believe that your agreement was that part of his job would be to do those things to your standard. His actions suggest that he does not view his job the same way you do.
4. Your DH has been a SAHD a long time. His actions demonstrate that he no longer finds this role fulfilling or sustainable on its own, and that he needs time/space/energy for stuff that is just him (see 2, above). However, because his "job," as defined within your family, is still SAHD, he is attempting to accomplish 2 on top of all of his existing obligations, which leaves him short on time/energy for 1 and 3.
So, really, you are right that something has to give, but you are wrong to approach this from the perspective that the "fix" is for you to persuade your DH to spend less time on 2 and more on 1 and 3. He is *not happy* with solely being a SAHD. 8 years ago, you guys both probably went into this division of labor believing that it would work for both of you. Then life happened, and it isn't working for him any more. So the real "fix" is to restructure your arrangement to lift some of the burdens that go with the SAHD job so that he can devote some time to his own passion while still having time/energy left to spend with you as a family and a couple.
The obvious starting point is the housework. My rule in my house is "he who has the higher standards is responsible for making sure things are done to his satisfaction." I.e., agree on a very basic level of acceptability; anything more than that is on the person who cares more. In my house, this means that I am the one who gets to worry about making nutritious meals. In your house, it would mean that cleaning above basic sanitation levels is on you. Or make the whole issue go away by hiring cleaners (my chosen solution).
But clearly, lifting the cleaning duties is not going to solve the problem, because he is already not cleaning to your standards. So if you want time with him, then you need to figure out a way to ease some of the other SAHD duties. E.g., daycare, babysitting, preschool. Give him more time during the day to do his classwork and homesteading, so that you guys can enjoy family time when you are home for work.
Note that I am not saying this all has to fall on you. Your DH may be one of those people who will gladly putter and tinker to fill all available hours, and to the exclusion of all else. So if he is being that guy, it is reasonable for him to cut that back some. But my point is that that is not the starting point for the discussion -- he has just resumed this after years of doing the SAHD job exclusively! You need to approach this from the mindset that acknowledges that *he is not happy* as a full-time SAHD and that he legitimately *needs* this other stuff to be happy, and so your job as a couple is to figure out how to make that happen, because any plan that leaves one of you unhappy long-term is not an acceptable solution. So your initial question can't be how to get him to cut back on "his" stuff to focus more on what you want; it *has* to be "how can we renegotiate the division of labor to free up more time so we can both get more of what we need to be happy?"