Bought NE rowhouse. Then took it down to party wall brick and joists (some of which we also removed), ripped off rear wall and added 20x20 extension on 3 levels and underpinned basement to get extra 3 feet of ceiling height. It was a MASSIVE project. It was a lot of work. It was stressful. I do not for a moment regret it.

1. No regrets at all. We worked with an architect and then I made tons of changes throughout the process to get exactly what I wanted. Dream kitchen (400 square feet), 10x3 foot island in single piece of stone, switches exactly where I want them, massive windows, killer insulation throughout, reclaimed red oak floors sanded and stained in place in a color I created myself, power everywhere and precisely where I wanted, network cables home runned to my server room, built in speakers, etc.
2. Broke ground as planned...and that was the last time we were on schedule. Fortunately we were living in our old house while the work was done. Quoted time was 6 months. Was almost 11 months from breaking ground to when we occupied.

It is WAYYYY cheaper to do all the renos at once. Trades are expensive to bring in one at a time; you get much more for your money at scale. You can also do the reno the way you want without having to make concessions to living there.

Happy to provide more context and info if you want to PM me.