As for the first rumor, I have NEVER heard of that happening. Unless we have a few dozen people who have been to WDW in the last month or so, and they have skipped an ADR and had the remainder of their ADRs canceled, I wouldn't worry about this. It seems a little extreme for Disney to do something like that; charge CCs, etc., maybe, but not arbitrarily canceling every remaining rez.
As for the second rumor, I, myself, as a test, was able to book four ADRs within five minutes of each other for dinner: CDF, LC, ND & Marrakesh, all between 6:55 pm and 7:00 pm on the same night. There was nothing to prevent this except a caution that popped up, stating if these were duplicates "to please" cancel one or more; that if these were for split parties, to continue booking as usual. The new system does not appear to mind whether you double or quadruple book. It's a shame. I was hoping they would crack down on this. Incidentally, I canceled those test ADRs. I'm not that cruel to my fellow DISers.
Nope, you don't need a credit card unless you are booking CRT, or California Grill, etc. Places that need a CC guarantee. 
