Wow, first of all thank you for the kind answers and suggestions.
I regularly develop BW and I also have some experience with C-41 (though I have no idea how relevant the latter still is, as the last color roll I developed was 15 years ago or so, when I was still somewhere in my late teens).
What I plan to do is partially fill my bathtub with hot tap water, put all the paraphernalia in, and let it all level to 38C. I hope this setup will have enough inertia to keep things at a constant enough temperature throughout the development. If needed, I could add more hot tap water.
Yes, the main slide film will be Velvia (mostly Velvia 50), but I think I will indulge myself , and sample a few other brands. Astia (though a diferent animal) and Ektachrome VS are high on my list.
I'll try to shoot and develop a few rolls before going on holiday, to see how they come out.
Do you have any agitation tips? (I will be developing 120 film in a regular 2-roll Kaiser tank)