Can´t comment on Tetenal, but it is common for manufacturers to give very conservative estimates of shelf life of chemistry. Developer or reversal won´t deteriorate in one week, although Fuji suggest they will. We talk about two months at least in normal conditions. Much more serious problem with all kits is that it is quite hard to estimate the correct time for first developer if it is reused. Unfortunately, the professional chemistries for E6 are available only in very largu quantities, and for standard process. there are Bellini and Jobo kits in the European market. First developer is not available in reasonable quantities for home use separately - except for Cinestiill. These developers seem to be nonstandard though, and many people have had issues with their E6 kits. I personally use Bellini at the moment, but limit its use to about 8 rolls maximum. They say it is good for 12 per liter, but the results are unacceptable for my standards if the kit is used that much. The highlights will be too dark if the 1st dev is pushed too far.
For the price of slide film, one good solution is buying movie stock, and bulk loading. At least in Europe, some of the movie stock suppliers sell also 100 ft rolls of Ektachrome, if 400 ft is too much. It is much cheaper compared to the Alaris version. The future of Fuji slides is a mystery - I like the colors of Provia more than those of Ektachrome, although both films are superb in overall quality. Velvia is a bit too saturated in my opinion, although it is very good for some scenes.