1) I would pre-heat more. You also have to bring all the plastic, the basins, the chemistry in temperature. The motor does not "suffer" for preheating as there is no chemistry in the tank, so it is very light to rotate. I pre-heat for 20 minutes or so.
2) I now pre-rinse with two 30-seconds baths. I recover the water in a graduated cylinder and measure it to see if there is any leakage before beginning treatment. Jobo tanks can be tricky, you thing they are tightly closed when they are not. I use 7:30 for the first development and the first use of chemistry. I use one-shot chemistry which I actually use twice (see below). The second time I develop for 8:00. Rotating processors seem to need a bit more time than other techniques. Notice that I count developing times from when I start pouring to when I start emptying. Times are for Sensia 100 ISO exposed at box speed.
3) Just don't use too-cold water. Water at room temperature is perfectly right for mixing.
4) If you have normal quality water you should use normal water, and use distilled water only for the final bath. That's what I do. If I had water of dubious quality I would use cheap oligomineral water (low total mineral content) for all baths except the final one.
5) Good question! I have this doubt myself. I tend to develop 1 roll at a time in a Jobo 1520 (140ml) but just pour in 250ml for every wash. That's because it's easier, as I fill the graduated cylinders in the Jobo CPP-2 without measuring how much water I pour in. I suppose that while rinsing there is no problem if you use too much water. Maybe the rinsing is a bit slower (less swirling) but I always wash very carefully anyway.
6) The majority seems to favour inversion. Jobo literature recommends inversion for slides IIRC. I use inversion. I disable inversion during the pre-heat, which I operate at F speed (slow). Before beginning I activate inversion and set the speed slightly beyond P.
7) Probably yes. I never developed anything by myself which was not Fujichrome. I found that 7:30 is right here. I set my Jobo at 38.3° and let temperature stabilize at 38.3° (it will oscillate anyway a bit, around 0.4° above and below, even after two hours of stabilization). That means chemical reactions should happen at around 38.0°. It's not so important if the temperature bath is 37.8°, 38.0° or 38.2°. What's important is having a repeatable procedure. Don't worry too much about the time. Start with 7:30 and you will have acceptable results, I do believe. 30" plus or minus is a very minor tweaking that you will make observing results. "Fine tuning" so to speak.
8) Two schools of thought here. One says never have the plastic reels touch the final bath. Jobo belongs to this school. The other says don't worry about that, just wash the reel carefully after treatment. I belong to the latter. I open the tank, take the entire reel, put it slowly inside a glass container with final rinse, agitate the reel for 20", let the reel in the bath for a further 1 minute or more, than "fish" the reel and while keeping it horizontal I separate the two halves and take away the top one. I now clip the clip on the extremity of the film, and raise it to the drying cupboard. I pay attention not to touch the film with my hands, and normally manage to do so.
9) The instructions of my chemistry (Ornano E-6 kit) say I can reuse one time the one-shot chemistry, with the only precaution that I should prolong 1st development by 30". If you do it, it's better if you:
- Make the second treatment within a short time from the first. I do it within 24 hours;
- Introduce a wash between bleach and fix (if you intend to reuse the chemistry).
Using blix I would just observe results.
I've read reports in one Italian forum of somebody who reused one-shot chemistry way beyond recommended times. You should evaluate if the results satisfy you. Keep in mind that rotative processors make the chemistry swirl, and therefore oxidise, quite a lot.
Read the instructions for your kit. The instruction for a Kodak E-6 kit said no reuse was possible. Again, that might only mean that there is a very slight reduction in quality between first and second soup. Considering the high cost of your chemistry, I would try to use it at the very least two times for one-shot preparations. Check that the producers recommends one-shot use of their chemistry.
10) Don't worry about 15" differences. IIRC 1 minute corresponds to less than half a stop difference. When you have a big tank (many films) it takes more time to pour chemistry in and out. So maybe that explains the difference.
11) In theory yes. In practice some people reports strange effects. If you do, it's probably better if you pre-wash your films (you take away that kind of washable chemistry that you see colouring the pre-wash water, you don't know what side-effects that might have). Commercial laboratories soup all slides in the same tanks so I think it is basically doable.