Since you also went through the process yourself: Can you say something about the expected 'man-days' for the work? How long did you, for example, work on the electrical installation?
Your list is quite long. Since we did not do all of these jobs, only info on the work we did (140m²)
Drilling electrical slots and holes for sockets: pre-planning, marking, measuring: 1 day Then we spent another day, the three of us, going through the house. One with the double-groove router, one with the rotary hammer, and one with broom and construction bucket. Pulling cables took another day for two people, plastering as well, and connecting sockets went quickly. So 8-10 man-days.
a1: Attic ceiling, walkable: in hindsight, I would do wood fiberboards with a compressed surface, you just need to lay them out. For 50m² one day. We have step-resistant rock wool with chipboard, which is 1. more expensive and 2. an extra step.
j: Basement ceiling. We just doweled ours, 10cm rock wool. The corners, edges, and pipes cause the most work. For 56m² basement, two of us needed 2 days. We installed the electrical wiring later on the walls surface-mounted in the basement.
l: Heating. How do you want to install baseboard heaters and keep the old pipes inside at the same time? For that, new pipes need to be run surface-mounted. Why add additional baseboard heaters at all? With the old boiler, low supply temperatures don't help, and the wood stove doesn't care either. Closing niches depends. For small niches simply use aerated concrete on the screed and brick it up. For larger ones, better remove the screed. Do not leave air gaps, seal everything with mortar! I closed all 5 niches in our house alone in one day. In general, I didn't want to solder or press copper pipes, etc. Therefore, we had all the water and heating pipes installed professionally. Learning that would have taken longer and it's not that expensive. You can also simply use regular convectors as radiators, they operate at 70/55 and even 45/35 °C. The shape, size, and number of radiators really depend strongly on the building and individual rooms as well as the desired room atmosphere. Maybe research that beforehand. We installed large heating walls in the living area, which have a nice combination of radiant heat and convection, underfloor heating in kitchen and bathroom, and simple convectors under the windows in the sleeping area.
m: Tearing down walls. Tearing down is easy if it is not a load-bearing wall. If it's not the entire wall, first pre-groove the edge as deep as possible on both sides with a double-groove router, then the edge becomes noticeably smoother and easier to finish without much rework. We had it done by someone else, but our mason was alone and took at most one day for a 1.5m wide section including concrete lintel and applying base plaster. So count on 3 man-days as a layman. The most work is the debris removal, a whole lot comes out!
Plastering work: We did all ourselves, no rocket science. When plastering completely new, definitely use plaster beads, otherwise it won't be straight! We applied new fine plaster all over the house (lime fine plaster and partly lime smoothing). I took about 10 days just by myself.
Topic windows: Material costs for plastic windows are probably more like 150€/m² (at least double-glazed with warm edge). Installation of small windows you can do yourself quite well; with large window fronts, front doors, or similar, it's another story. You also need the strength for that. We had it done – but the installers were bad, and in the end, I worked forever until everything was right.
Topic sealing: Don't underestimate material costs. If you have screed in the basement, you have to prep the edges before interior sealing, and the sealing must extend onto the footing slab. I can't say anything about the time involved, we did that from the outside. Applying the sealing itself goes quickly. Just don't slack off on sealing! Follow the guidelines and especially ensure a clean, adhering substrate.
For 140m² including screeds, heating, electricity, roof insulation, all floors, interior doors, plaster, windows, masonry work, new bathroom including tiles and sealing, roof insulation, we needed from early November to mid-April. Every weekend plus 3 weeks of vacation, always two of us (me and my father), sometimes three. Because it was winter, only moderately heated and it got dark early, my wife and I had a baby, and my parents always had an hour's drive, we only worked roughly from 8 a.m. to 3/4 p.m. But you can't tolerate more for long, otherwise, you need breaks. A lot of time also goes into material shopping. I always did that Friday afternoon, as I was alone then and would hardly have accomplished anything in the house.
We did the basement only in summer.
I would think carefully about what you can do yourself and for what you would need much longer because you first have to learn it for only a small part of the work. Then look at how much time and time pressure you have.
Have fun and good luck